Alfred Russel Wallace: the "red-headed stepchild" of Evolutionary Theory?

“In 1858, Alfred Russel Wallace, aged thirty-five, weak with malaria, isolated in the Spice Islands, wrote to Charles Darwin: he had, he said excitedly, worked out a theory of natural selection. Darwin was aghast--his work of decades was about to be scooped. Within two weeks, his outline and Wallace's paper were presented jointly in London. A year later, with Wallace still on the opposite side of the globe, Darwin published On the Origin of Species.”

Peter Raby in “Alfred Russel Wallace: A Life”

Alfred Russel Wallace (1823-1913) was born in southeast Wales to a middle-class couple of modest means. Alfred suffered from poor health throughout his childhood, as did his other siblings; 4 out of 5 of his older sisters died before the ages of 22. By the time he was 14, he was forced to drop out of school and move to London and later Bedfordshire to live with his older brother William due to economic hardships within his family. It was here that he picked up a number of trades including draft and map-making, building design and construction, mechanics, and agricultural chemistry.

He also began taking an interest in natural history during this time, particularly in the areas of botany, geology, and astronomy.

In 1843, he began a teaching position at the Collegiate School in Leicester. He became engrossed in the library and read endlessly on topics including natural history and systematic. A chance meeting with another young amateur naturalist and entomologist, Henry Walter Bates, furthered his interest in collecting specimens and contemplating natural history.

Fun Fact! Henry Walter Bates gave the first scientific account of Batesian mimicry in animals.

After his brother William died in 1845, he quit his teaching job and returned to surveying. However, surveying did not afford him the knowledge he sought, so he continued with his natural history-related activities. He was even made curator of the Neath Philosophical and Literary Institute’s museum.

Intrigued by a book titled “A Voyage up the River Amazon” by William H. Edwards, Wallace and his new comrade Bates decided to legitimize their amateurish inklings and launch a self-sustaining natural history collecting expedition to South America. At the time Wallace was 25 and Bates was only 23!

Visual mimicry of host nestlings by cuckoos

In this article, I will present the study “Visual mimicry of host nestlings by cuckoos” by Langmore et al. 2011. The biological model used here is the cuckoo, which is a brood parasite species. Brood parasites species lay their eggs in the nests of other birds and do not provide any parental care for their own offspring. This has a detrimental effect on the reproductive success of the hosts for several reasons. First of all, the parasite can evict the host offspring by removing host eggs from the nest, either the parasite female when it lays its eggs, or by the chick if it hatches earlier than the hosts chicks. Then, if the hosts chick stay alive, we will observe a diminution of the host nestling growth rate, because of a competition between the chicks for food and care. Because hosts are able to discriminate their offspring from the parasites offspring and then reject parasites' offspring, many brood parasites will try to increase the similarities between eggs and/or nestling parasites and their hosts' one to decrease the risk of rejection. With increasing fitness costs of parasitism, selection for host defenses increases, which in turn may force parasites to specialize and evolve fine-tuned adaptations that overcome a particular host’s defense. From brood parasitism results a coevolutionary arm race between hosts and parasites, and therefore a coevolution between them.

Coevolutionary mimicry in brood parasites is a counter-adaptation (i.e. result of coevolution between parasites and hosts) against host anti-parasitic response.

Here, we are going to focus on the visual part of mimicry of hosts nestlings by cuckoo parasites. Mimicry can be defined as an adaptation evolved by selection pressure from signal-receivers (Vane-Wright, 1980). It arises from a reciprocal interaction between two or more evolutionary lineages with each party selecting for changes in the other.

There are two types of brood parasitism, non-obligate and obligate. Non-obligate brood parasites lay eggs in the nest of conspecifics (i.e. same species) and in their own nests. Obligate brood parasites lay eggs in nests of other species and have completely lost the ability to construct nests and incubate eggs.

The three parasites species study here are Chalcites bronze-cuckoos, and their respective hosts. They are obligate brood parasites. The hypothesis tested here is whether the evolution of cuckoo chick discrimination by hosts of Australian bronze-cuckoos has reciprocally selected visual mimicry of host young by cuckoos sensory systems. The particularity of this study is the use of supposed bird criteria to assess the resemblance between hosts nestlings and parasites.

Methods

The species of bronze-cuckoos and their hosts studied were :

- Horsfield’s bronze- cuckoo C. basalis (primarily parasitizes Malurus hosts)

- Shining bronze-cuckoo C. lucidus plagosus (primarily parasitizes Acanthiza hosts)

- Little bronze-cuckoo C. minutillus (primarily parasitizes Gerygone hosts).

The study was conducted in Australia, at one site for every species but C. minitillus, studied at two sites, with two subspecies parasites of the same host.

After the location of the nests either by following adults or by searching for nests (for Gerygone nests), some of them were protected with a cage to avoid the predation by large predators, to minimize loss of data.

Spectral reflectance of nestlings' skin was measured (back and flange), and the nest irradiance spectra calculated.

Then, they analyzed the volume of avian color space that every individuals occupied, in order to calculate the level of color variation among and within the cuckoos and hosts. The more volume is occupied, the more variation there is.

The next step was a visual modeling to predict if a bird would be able to discriminate between two objects based on color (chromatic variation) or luminance (perceived lightness). I won't detailed the statistical analysis here.

Results

Chalcites cuckoo nestlings show substantial appearance variation between cuckoo species, but resemble strongly to their respective hosts. Especially, the variation in skin color was greater between cuckoo species than between cuckoo-host.

Figure 1. Representative photographs and mean+s.e. reflectance of the skin of nestling bronze-cuckoos (blue lines) and their hosts (pink lines). (a) Little bronze-cuckoo and large-billed gerygone. (b) Shining bronze-cuckoo and yellow-rumped thornbill . (c) Horsfield’s bronze-cuckoo and superb fairy-wren (n ¼ 17). (d) We also include a second host of Horsfield’s bronze-cuckoo, the purple-crowned fairy-wren M. coronatus

The visual modeling was used to assess if the nestling cuckoo was a better visual mimicry of its own host other host species. They found that the level of match between the appearance (skin color and luminance) of the nestling cuckoo and its host was correlated with the degree of host specificity :

- Little bronze-cuckoo almost perfect match with its host (specialist parasite of darkskinned gerygone hosts), an is significantly different from other hosts

- Shining bronze-cuckoo show significantly more similarity to both thornbill and fairy-wren hosts than to gergyone hosts. Intermediate host specificity parasites both thornbill and fairy-wren hosts (secondarily)

- Horsfield’s bronze-cuckoo present a similar degree of resemblance for every hosts. Specialized on fairy-wrens throughout its range, but secondarily exploit a range of other hosts.

- The rictal flange color of nestling bronze-cuckoos was more similar to their primary hosts than to non-hosts for all three cuckoo species.

- The rictal flange luminance shows no correlation between parasites and hosts for any cuckoo species.

Figure 2. The disparity (mean+s.e.) between bronze-cuckoos and their own hosts versus other hosts in (a,d,g) skin colour, (b,e,h) skin luminance and (c,f,i) rictal flange colour. (a–c) Little bronze-cuckoo; (d–f ) shining bronze-cuckoo; (g–i) Hors- field’s bronze-cuckoo. SFW, superb fairy-wren; YRT, yellow-rumped thornbill; LBG, large-billed gerygone. The arrow indicates the primary host in each graph. The asterisks indicate Tukey HSD significance levels (p, 0.05) with the bars below indicating the two species being compared.

Discussion

These results show the evidence of a visual mimicry to host young by cuckoo nestlings for the first time. Indeed, the experiments, by using a “bird point of view” and not only similarities in the appearance for human eyes makes this study different.

However, we need to make sure that the similarities observed are indeed coevolution in response to discrimination by hosts and not “simple” similarities. The necessity of making this distinction was pointed out by Grim in 2004 in his study “Mimicry vs. similarity: which resemblances between brood parasites and their hosts are mimetic and which are not?”. To be called “mimicry”, a similarity should be the result of a coadaptation, otherwise the similarity is cryptic (non-mimetic), and results from convergent evolution (Harrison, 1968; Mason & Rothstein, 1987). So we need to assess if the similarities are specific adaptations and counteradaptations, (2) adaptations resulting from other (non- coevolutionary) selection pressures, or just (3) by- products of some other – perhaps adaptive – traits.

Several processes might create similarities between hosts and parasites, and they are the same eggs similarities and nestling similarities (Grim 2004) :

1. Phylogenetic constraints : the similarity of egg and chick appearance is probably the result of common descent. This process is applicable for intra-specific parasitism.

2. Random matching : if the parasites have a large range of hosts. For example with passerines, which show limited inter-specific variation in the appearance of their eggs.

3. Spatial autocorrelation in the diet of hosts and parasites : environmental similarities could influence the coloration of both host and parasite eggs in the same way. This hypothesis is only applicable for eggs.

4. Nest predation : predation could select for an inconspicuous appearance in both host and parasite eggs and nestling (no evidence shown for nestling, but applicable in theory)

5. Egg replacement by competing female cuckoos : in this case the model is the host’s egg, the mimic is the egg of the first cuckoo and the operator is the second-arriving cuckoo.

6. Host discrimination : increase similarities with hosts eggs and chicks to avoid rejection.

Clearly, 1, 2 and 3 have nothing to do with coevolution, process 4 is crypsis, and only 5 and 6 are examples of mimicry.

The coevolution between Chalcites cuckoos and their hosts almost certainly has selected for mimicry of host nestlings by cuckoos because experimental studies show that (1) hosts of Chalcites cuckoos can reject parasite nestlings (2) chick rejection is a specific response to brood-parasitism, such that hosts show flexibility in their responses to nestlings depending on the risk of parasitism; and (3) non-mimetic nestlings suffer a survival cost. These results were found in previous study by Langmore et al. (2003, 2009).

As a conclusion, we can say that visual mimicry is a result of the evolutionary arm race between brood-parasites and their hosts, and that the degree of specialization of the parasite is correlated with the level of resemblance with the hosts.

Citations



[1] N. B. Davies and J. a Welbergen, “Cuckoo-hawk mimicry? An experimental test.,” Proceedings. Biological sciences / The Royal Society, vol. 275, no. 1644, pp. 1817-22, Aug. 2008.

[2] Davies and Brooke, “AN EXPERIMENTAL STUDY OF CO-EVOLUTION BETWEEN THE CUCKOO , CUCULUS CANORUS , AND ITS HOSTS . AND GENERAL DISCUSSION,” Journal of Animal Ecology, 1989.

[3] T. Grim, “Mimicry vs . similarity : which resemblances between brood parasites and their hosts are mimetic and which are not ?,” Society, pp. 69-78, 2005.

[4] O. Krüger, “Brood parasitism selects for no defence in a cuckoo host.,” Proceedings. Biological sciences / The Royal Society, no. February, Feb. 2011.

[5] N. E. Langmore, G. Maurer, G. J. Adcock, and R. M. Kilner, “Socially acquired host-specific mimicry and the evolution of host races in Horsfield’s bronze-cuckoo Chalcites basalis.,” Evolution; international journal of organic evolution, vol. 62, no. 7, pp. 1689-99, Jul. 2008.

[6] N. E. Langmore et al., “Visual mimicry of host nestlings by cuckoos.,” Proceedings. Biological sciences / The Royal Society, vol. 278, no. 1717, pp. 2455-63, Aug. 2011.

Honey, We Shrunk the Fish: Overfishing, Evolution, and the Threat of Permanent Ecosystem Change

Let’s say you are a big, healthy Atlantic cod off the coast of Newfoundland in the year 1985 and you are in your sexual prime. Your sap has risen and you and several thousand other of your slimy kin are piled onto a rocky reef, perhaps listening to Marvin Gaye, and getting it on in a frenzied orgy of spawning. There are tons of high quality forage fish to eat; the million eggs you just laid or fertilized are ready to carry your genes; things are going great. You might even be smoking a cigarette and sporting a self-satisfied smirk as you think about what a lovely thing it is to be a cod. Then a net the size of a football field sweeps you and your lovers away, your food source eats most of your eggs, and your great-great grandchildren all turn out to be runts and teen parents. This is your story.

The collapse of the cod fishery off the coasts of Newfoundland and Labrador (hereafter Northern cod) may be one of the sadder stories in recent environmental history. In 1962, the first year in which good data are available, there were an estimated 1.6 million tons of spawning cod off the northeast Canadian coast (Hutchings and Myers 1994). 1.6 million tons. It would take 212 Yankee stadiums with a 317 pound sumo wrestler crammed in every seat to equal that mass of fish. It might not be surprising that almost everyone thought that it would be impossible to overharvest such a population. Alas, almost everyone turned out to be wrong. Catch rates plummeted throughout the late sixties until the early nineties along with a sustained decrease in the amount of spawning cod biomass (Figure 1). By the time Canadian resource managers finally placed a moratorium on the fishery in 1992, only 22,000 tons of spawning fish remained, a paltry figure that equates to less than three stadiums worth of fish. Optimists who believed that time would heal all, and that cod populations would certainly recover have also turned out to be wrong. The processes of quantitative evolution may be part of the reason why.

A Thought Experiment

To understand how fisheries can change the genetic makeup of a population over time, let’s perform a thought experiment. You’ve got a very large aquarium of genetically and phenotypically diverse fish in a room with a very clever cat. The cat non-selectively catches a certain proportion of the fish in the tank. Those fish that the cat eats before they have a chance to spawn have a fitness of zero, and those fish that spawn before eaten have a fitness greater than zero. As the experiment progresses, it isn’t difficult to see that the fish population will be selected to breed at a younger age, since the penalty for slow maturation will often be death without hope of passing on genetic material. The change in your fish population may occur faster than you might expect, given that it is estimated that about 20-30% of variation in life history traits of fish is heritable (Kuparinen and Merilä 2007). What may be even more surprising is that all of your fish are gradually becoming smaller, even though your cat is being completely non-selective in which fish it eats. This is because the growth of fish declines when a fish becomes sexually mature since energy is being shunted from growth toward reproduction (Conover, Munch, and Arnott 2009). The outcome? Over time all you’ve got is a tank full of small, sexually precocious fish.

We Are the Cat (But Worse)

The parallels between the thought experiment above and fisheries are obvious. If fishing pressure is intense enough, and little gene flow occurs among populations, and if fish populations have sufficient genetic variation, then early maturation and small size will eventually dominate a population. The problem with this parallel is that fishermen, unlike the cat, are highly selective in the fish they target. Fisheries most often target large individuals, meaning that an overt directional selective pressure is being placed on fish relating to size, in addition to the pressures nudging fish toward early reproduction (Kuparinen and Merilä 2007). In the case of the Northern cod fishery, both intensive selective pressure on size and inadvertent selection on breeding age appear to have occurred. Age and size at first breeding was seen to plummet before the closure of the fishery in 1992, and as expected in a scenario of a genetic change in the population, these parameters have not recovered since. It appears that the selective pressures of overfishing have changed Northern cod into a small, early breeding fish. Add the pressures of a changing ecosystem, and you have an even greater problem.

Permanent Ecosystem Change?

Marine ecosystems are often thought of as a zero sum units. When large quantities of a top predator, such as cod, are removed, other sources of biomass will fill the vacuum and may radically alter the structure of the ecological community (Frank et al. 2005). The prey species of northern cod, including Atlantic herring and crab species, have skyrocketed over the same time period that cod have collapsed, and large scale changes in the plankton community have also occurred (Frank et al. 2005). These changes may actually be inhibiting the recovery of cod stocks through several mechanisms. In a curious case of predator-prey role reversal, burgeoning herring populations are thought to be dining on cod eggs and juveniles, causing undue mortality on cod well before they are able to spawn (Swain and Sinclair 2000). Changes in phytoplankton and shrimp abundance may also have led to decreased foraging efficiency, and thus slower growth for cod. These radical changes are occurring in an environment where cod are also hamstringed by genetic shifts toward early reproduction and slow growth. The frightening upshot is that Northern cod maybe be permanently relegated to only a bit role in the ecosystem in which it was once the lead player.

Evolution and the Path to Prevention

It is unclear whether the Northern cod population will ever recover to its former level, but the lessons learned from its story are being applied to other areas in hopes of preventing further fisheries collapses. One option that is currently de rigueur is the establishment of marine protected areas, where little or no fishing occurs. The idea is simple. If fishing has a tendency to create genetic changes in breeding age and size in populations, then sources of fresh genes that have not been altered by fishing selection can counteract these shifts through genetic mixing. For these protected areas to work however, they must be large enough to maintain genetic diversity and close enough to harvested populations to ensure sufficient interbreeding. Another option is to establish minimum and maximum size length limits to both ensure that individuals are always able to breed at least once before harvest, and to maintain the genetic variability within the largest members of a population. Though it might be too little for the Northern cod fishery, change is not too late for other marine areas. Our disregard for evolutionary impacts of fishing in Northern cod can at least be partially amended by our application of evolutionary concepts toward maintaining genetic diversity in other harvested fish species across the globe. We’ve learned that 212 Yankee stadiums worth of fish is easier to lose than you’d think. With well-considered fisheries practices in the future, it is not something that we should lose again.

Conover, D.O., S.B. Munch, and S.A. Arnott. 2009. “Reversal of evolutionary downsizing caused by selective harvest of large fish.” Proceedings of the Royal Society B: Biological Sciences 276(1664):2015–2020.

Frank, K.T., B. Petrie, J.S. Choi, and W.C. Leggett. 2005. “Trophic cascades in a formerly cod-dominated ecosystem.” Science 308(5728):1621.

Hutchings, J.A., and R.A. Myers. 1994. “What can be learned from the collapse of a renewable resource? Atlantic cod, Gadus morhua, of Newfoundland and Labrador.” Canadian Journal of Fisheries and Aquatic Sciences 51(9):2126–2146.

Kuparinen, A., and J. Merilä. 2007. “Detecting and managing fisheries-induced evolution.” Trends in Ecology & Evolution 22(12):652–659.

Swain, DP, and AF Sinclair. 2000. “Pelagic fishes and the cod recruitment dilemma in the Northwest Atlantic.” Canadian Journal of Fisheries and Aquatic Sciences 57(7):1321–1325.

Summary and analysis of the article: Evolution of pollen to ovule ratios and breading system in Erodium( Geraniaceae)

For this blog I read an article on the evolution of pollen to ovule ratios and breading systems in Erodium (Alarcon, 2011). Erodium is a genus in the Geranium family and has an interesting pattern of differential reproductive strategies. The article distinguishes two main groups of species within the genus: perennial species (living more than one year) and annual species (living for one growing season). Most of the perennial species have, in addition to a longer life span, a medium to high pollen to ovule ratio, dichogamous (gametes mature at different times on hermaphroditic flowers) and herkogamous (gametes are separated spatially from each other on hermaphroditic flowers, see photo to left) strategies, and are endemic to the Mediterranean. In contrast, annual species typically occupy disturbed sites, lack strong dichogamy or herkogamy, a low pollen to ovule production ratio, and a much wider distribution. The authors of the article attempted to answer three main questions: 1.) How did these different breeding systems evolve? 2.) Did the annual lifecycle and self-fertilization in the genus evolve together? 3.) How did geo-climate changes affected the evolution of the genus?

There are many different types of breeding systems in flowering plants. Because plants can have both male and female components on a single flower, different mechanisms have evolved to either ensure self-pollination or out-crossing (See right for self-pollinating flower. Notice how the anthers surround the stigma). For example, a flower might have the male component mature more quickly than the female component. This type of strategy (known as dichogamy) ensures out-crossing because the male and female components on the same flower are fertile at different times. Differences in the breeding systems of flowers have been described as methods of reducing or improving the likelihood of self-reproduction and/ or improving the efficiency of sex roles (Burd et al. 2009).

As a general rule, the amount of pollen produced per ovules produced per flower is similar to the idea of clutch size in animals. Each gamete produced has a resource cost associated with it as well as a benefit as long it contributes to a fertilized zygote. But, depending on the variability of pollination success, it may be more beneficial to produce more pollen per ovule in some cases, and less in others.

The basic distinction between annual and perennial species (the amount of time to life cycle completion) shows that both r and k selection pressures are present. It may be more beneficial for plants present in a rapidly changing environment to produce more offspring over a shorter period of time (annual, r-selection). However, if the environment is not changing rapidly, a plant may live many years and only reproduce when optimal (perennial, k-selection). Another study I looked at shows that a strong r-selection on annual flowering plants in general gives more benefit to self-fertilization than out-crossing (Snell, and Aarssen, 2005).

In the article I read, the amount of self pollination was found based on the amount of viable seeds produced when the flowers were enclosed in pollen-proof bag. In addition, the amount of pollen produced per ovule per flower was counted. The authors of this article found that in Erodium more pollen produced per ovule is typically a sign that the species is focusing on out-crossing, or mixed mating (outcrossing sometimes and self-fertilizing other times), whereas a low pollen to ovule ratio is something to be expected from obligate self-fertilizing species (This makes sense if you think about it because if fertilization doesn’t require a pollinator, much less pollen is wasted; and therefore less is needed). Using a phylogeny of the genus, in conjunction with breeding systems and pollen/ovule ratios, they found that an annual self-fertilizing trend was present in basal members of the genus before members of the species had settled in the Mediterranean (see phylogeny to the left; the key in the top left corner refers to the pollen/ovule ratios). This is an important discovery because many scientists had hypothesized that self-fertilization was an “evolutionary dead-end”, according to Alarcon. Although self-fertilization has its consequences (see F and H text on inbreeding depression), it also has several important benefits. Because a pollinator isn’t needed, self-fertilizing plants can colonize barren land (where no pollinator would have interest in visiting). Once the area is settled, the plants could diversify through mutations preventing self-fertilization. It appears that this was the case in Erodium. The self-fertilization strategy was present in ancestral species and then was reduced or lost in some lineages. This could be accomplished by increased dichogamy or herkogamy.

Through observing pollinator visits per species, Alarcon found that species which competed for pollinators have larger flowers and more separation of male and female sexual organs. In areas where pollination events were rare, species had smaller flowers, and more overlap between mature male and female sexual organs. The latter strategy is hypothesized by Alarcon to be due to a shifting fitness peak: outcrossing is beneficial when pollinators are present; self-fertilization is beneficial when pollinators are absent. Slight changes in the degree of herkogamy and dichogamy may have allowed species to adapt to the presence or absence of pollinators during periods of climate change in different areas. Towards the end of the article, Alarcon mentions that the phenomenon of switching between self-fertilization and out-crossing was common amongst flowers at the time (possibly for the same reason of changing fitness peaks).

In summary, this article gives a classic example of multiple and shifting fitness peaks. These peaks occur based on r and k selection pressures. The r selection peak favors fast reproducing individuals with short life spans. Whereas the k selection peak favors optimal reproduction and a longer life span. These two fitness peaks shifted depending on available pollinators in a time of variable seasons and climate. If there were no pollinators, then individuals with pollen-efficient small flowers, as well as less herkogamy and dichogamy, left more offspring than other members of the population. If there were many pollinators, then individuals with the largest/showiest flowers with ambient pollen production could compete for pollinators. These individuals could also reduce the amount of self-fertilization by increasing the degree of herkogamy and dichogamy. If the pollinators were unreliable, then a good strategy would be to have self-fertilization occur later in life (which has been observed in mixed-mating members of the genus). This strategy gives the plant a chance to outcross in one part of its life, while keeping self-fertilization as an option. Self-fertilizing individuals have the advantage of assured pollination, and therefore may be able to colonize disturbed lands. The ability to easily reduce the amount of self pollination once the pollination community becomes established appears to have been a major key to the success and prevalence of the genus.

Sources:

Alarcon, Maria L., C. Roquet, J. Aldasoro. 2011. Evolution of pollen/ovule ratio and breeding system in Erodium (Geraniaceae). Systematic Botany 36: 661-676. http://www.bioone.org/doi/full/10.1600/036364411X583637

Burd, M., T. L. Ashman, D. R. Campbell, M. R. Dudash, M. O. Johnston, T. M. Knight, S. J. Mazer, R. J. Mitchell, J. A. Steets, and J. C. Vamosi. 2009. Ovule number per flower in a world of unpredictable pollination. American Journal of Botany 96: 1159–1167.

Snell, R. and L. W. Aarssen. 2005. Life history traits in selfing versus outcrossing annuals: exploring the ‘time-limitation’ hypothesis for the fitness benefit of self-pollination. BMC Ecology 5: 2.

Web Resources:

More information on plant breeding systems: http://www.sciencedirect.com/science/article/pii/S0960982206019178

Website of a cool botanist (check out the publications in the evolution and sexual systems categories)

http://www.sysbot.biologie.uni-muenchen.de/en/people/renner/website.html

Male Biased Dispersal in Cougars

Over the past two years, I have been studying cougar ecology and prey relationships in northeast Oregon. During this time, one of the most fascinating aspects of cougar ecology that I witnessed was their ability (and propensity) for long distance dispersal. The long distance dispersal ability of cougars has recently garnered national media attention. Despite the absence of established cougar populations east of the Mississippi River, two cougars have recently been documented (unfortunately due to their deaths). One cougar was shot in a Chicago suburb in 2008 and another cougar was recently run over in Connecticut. Genetic evidence confirmed both of these cougars originated in cougar population residing in the Black Hills of South Dakota – indicating these individuals dispersed at least 1,600 and 2,500 km, respectively. Long distance dispersal is not an uncommon for cougars, with dispersals of over 1,000 km previously observed (Thompson and Jenks 2005, Stoner et al. 2006). While dispersal, including long distance dispersal, is a common event for cougars, there is a very strong sexual bias in dispersal patterns. Upon reaching independence, female cougars tend to be philopatric (i.e., establish a territory within or adjacent to their natal range) and rarely make long distance dispersal events. In contrast, sub-adult, male cougars appear to always disperse a substantial distance from their natal territory (Sweanor et al. 2000). In fact, as of 2001, no study had documented a single instance of a sub-adult, male cougar establishing a territory that overlaps its natal range (Logan and Sweanor 2001).

For dispersal to be advantageous, it should increase the fitness of the dispersing individual (Morris 1982). However, survival rates of dispersing cougars are very low (Logan and Sweanor 2001), suggesting individuals would be better served to stay within their natal territory. This raises the question, ‘Why do male cougars disperse and female cougars typically stay close to their natal ranges?’. Several hypotheses have been proposed to explain male biased dispersal in polygamous, large mammals: 1) competition for mates, 2) competition for resources, 3) avoidance of inbreeding (Sinclair 1992), 4) higher cost of female dispersal (e.g., lower survival),and 5) increased breeding opportunities for dispersing males (Pusey and Packer 1987). Below, each of these potential hypotheses will be addressed based on existing knowledge of cougar ecology.

Is baculum length influenced by sexual selection?

The sexual selection was defined by Darwin in 1871 as the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction. It can be divide in two components. The first one is the pre-copulatory selection, which happens before the copulation via male competition, and via classic female choice for a mate. The one we are interested in is the postcopulatory selection, which cover all the events during and after the copulation. We can make an analogy with the precopulatory selection : the male-male battle of the pre-copulatory selection is equivalent to the sperm competition, and the classic female choice is similar to the cryptic female choice for the spermatozoa. The sperm competition occurs when the sperm from two or more males compete to fertilize a set of ova (Parker 1970; Birkhead & Møller, 1998).

The postcopulatory sexual selection is known to be a strong selective force driving the evolution of behavioral and morphological sexual traits (Andersson 1994).

The genitalia structure studied here is the baculum, the penis bone present in some species of mammals within the following orders : Chiroptera, Rodentia, Carnivora, Primates. The development of the baculum is highly variable among species, a characteristic which allows us to think that post-copulatory selection could be a factor that influence its morphology. Indeed, even closely related species show a great diversity of the baculum length and shape. Here, we are going to focus on baculum length.

Because of this diversity, the baculum function remains uncertain. Four main hypotheses are actually proposed : prolonged intromission, induced ovulation, vaginal friction, and indicator of genetic quality in males (Lariviere and Ferguson 2002).

The first hypothesis suggests that the baculum assists in sperm transport. This can lead to an increase of the baculum length in species which prolong intromission into the post-ejaculatory period (Dixson 1987) and in species that have a single prolonged intromission instead of several short ones. The distal head could also contribute to displacing or damaging sperm from previous males (Fairbairn et al. 2003).

According to the second one, the additional rigidity provides by the baculum could also be a way to stimulate the reproductive tract of the female to induce ovulation, and so increasing the likelihood of successful fertilization. The vaginal friction hypothesis could happen when the sexual dimorphism is strong, the baculum could help to support the increasing friction due to a relative small vagina opening by providing additional rigidity. Therefore, these hypotheses - except the last one - are not supported by everybody, but no better explanations can actually be found.

How Evolutionary Patterns Helped Find the Gnarliest Bird You’ve Never Heard Of

Here is how to make a model of a Kittlitz’s murrelet: take a nerf football, stretch it out lengthwise until its about 10 inches long, give it paintjob more or less like a dirty ashtray, throw on some stubby wings capable of sustained flight over 100 mph (which are also excellent for “flying” underwater), add a pair of webbed duck feet, and voila, you have a passable model for one of the strangest members of the seabird family Alcidae (Photo: J. Lawonn/USFWS). If you extend the model further, place your model atop a single giant egg on a steep slope of rocks on the flanks of a tall mountain, all preferably within sight of a huge Alaskan glacier. Really. In breeding ecology, behavior and plumage, the Kittlitz’s murrelet (KIMU) is one of a very small clade of supreme oddballs, the Brachyramphini, within the Alcidae, a family that otherwise shows remarkable similarity among species. Like the KIMU, all alcids share a similar body plan and forage exclusively at sea, and all have wings that are optimized for both fast flight and swimming efficiency. But that is where the similarities end. All alcids besides the Brachyramphini have a penguin-like black and white “countershaded” plumage pattern, nest colonially (and conspicuously) immediately adjacent to the sea, and breed almost exclusively on islands or cliffs that are inaccessible to terrestrial predators.

I began studying KIMU breeding biology in Kodiak, Alaska, in 2008 as part of a conservation effort to determine the causes of a dramatic population-wide decline that had been detected by boat-based surveys. Through the course of my research I have used the extreme phenotypic differences and the evolutionary relationships apparent in the Alcidae, as well as inferences made from patterns in convergently evolved species, to make predictions about emerging aspects of the breeding ecology of KIMU, and make hypotheses about this intriguing species.

The role of Climate Change in creating "plastic" amphibians

What does it mean to be plastic?

Plasticity refers to the variation in phenotypes under certain environmental conditions. This means that

one genotype can translate into multiple phenotypes based on the environment. Phenotypic plasticity is widespread in nature, and can significantly alter the relationship between organisms and their [abiotic and biotic] environment¹.

Figure 1 shows how juvenile grasshoppers (S. lineata) express density-dependent phenotypic plasticity in coloration.

The evolution of plasticity

The profile of phenotypes produced by a genotype across environments is known as the “norm of reaction”. It is often described by a curve that relates the contribution of environmental variation to the observed phenotype.

The level of phenotypic response to environmental change is determined by natural selection and can allow a given species to exploit novel environments or provide protection from others.² Just as in any heritable trait, genetic variation is required for the evolution of plasticity. Optimal norms of reaction can be achieved, but similar to Simpson’s Adaptive Landscape, they are dependent upon the ratio of selection and mutation and the amount of genetic variation available.

Conservation Biology and Evolution

Conservation Biology and Evolution

Conservation biology is an eclectic field of research drawing from fields of biology such as evolution, ecology, population genetics, and phylogenetics with the goal of protecting and conserving biodiversity on Earth. Among these fields, the study of evolution has vastly influenced conservation biology and made the field possible in many ways. Evolution played a key role in changing our mindsets to a point where conserving biodiversity made sense. It also gave conservation biologists the tools needed to analyze populations and communities. In addition, the process of listing rare species is dependent on theory provided by evolution.

Evolutionary theory changed our mindset about our role in nature

If you think about how humans viewed their role in nature before evolutionary theory became ubiquitous, you will find that it was fundamentally different the way we view it today. For example, Aristotle’s scheme for classifying life conveyed the idea that all life is organized as a gradient from simple to complex with humans being the most complex form of life. Although several early philosophers, such as Lao Tsu (the founder of Taoism), encouraged the concept of conservation, it wasn’t until there was a paradigm shift in the way that we view life on earth that conservation biology could really happen. In fact, even with early naturalists, rare species were specifically sought out because they were considered valuable collections (Farber). Philosophically this paradigm shift consisted of several realizations: the earth is old, life changes over time, the degradation of teleology as a form of reasoning, and humans are a part nature (Bowler).

Although Charles Darwin’s mechanism of natural selection was not initially well accepted, once his ideas were synthesized with those Gregor Mendel there was an explosion of new research. Scientists were beginning to understand concepts such as what causes invasive species to proliferate, how changes in the allele frequencies happen in populations, and overall more about the diversity of life. Many of these fields of research are what conservation biology draws upon. When Theodosius Dobzhansky said that “nothing in biology makes sense except in the light of evolution”, that certainly includes the field of conservation biology.