The authors start off the article by explaining that the toothed whales, or odontocetes, help form one of the three independently evolved peaks in brain size among mammals, with the other two peaks being formed by the elephants and primates respectively. All three of these groups of animals have incredibly complex and rich social lives, and many researchers have been able to make countless connections between these groups than they thought they could previously. The article goes on to describe many types of odontocete societies, including dispersal patterns in killerwhales (Orcinus orca), which apparently are quite distinct when compared to the dispersal patterns of terrestrial mammals. These killer whales travel in pods, staying with their mother, even into adulthood, with neither males nor females dispersing. These masses of whales are called stable “matrilineal groups,”defined as “a set of animals which have consistently stronger associations with each other than with other members of the population over periods of months to decades (1).” This killer whale example shows a difference when compared to many terrestrial mammalpopulations, where usually the males and/or females eventually disperse away from the family in order to live and reproduce away from close genetic relatives, establishing new territories.
Another interesting social system the authors discuss is that of Baird’s beaked whales (Berardius bairdii). These beaked whales, or ziphiids, live in deep ocean waters, and get their name from a distinctive pair of “battle” teeth found in most male species, with some exceptions being Baird’s beaked whale (see picture below (3)). In mostof the beaked whales, only males have these so-called “battle” teeth, and many have thought they wereto be used for male-male combat. However, in Baird’s beaked whale, both males and females share this common characteristic. Males in this species mature faster than females (an average of 4 years earlier), and also can live up to 30 years longer (1). These differences in the sexes imply a male-biased sex ratio among adults. However, some hypothesize that “the lack of sexual dimorphism in Baird’s beaked whales, the higher female mortality, and excess of mature males over females all suggest that males may be providing significant parental care (1).” I thought this was interesting because in many species that we consider “unintelligent,” the females provide mostof the offspring care, so this is yet another connection to many types of terrestrial mammals such as primates, where both the male and the female provide offspring care, with the male providing more care than usual.
I believe that one of the most interesting and amazing passages of this article discussed how closely related dolphins and chimpanzees were in terms of their social structures. Inshore dolphin species show something called “fission-fusion” grouping patterns, where the social “group” sleeps in one locality together, but forage in small groups going off in different directions during the day (2). This society is remarkably similar to chimpanzees, and elicited comparisons based on the similar “patchy” distribution of fruit and fish. Another common pattern in the social structures of both chimpanzees and bottlenose dolphins is that they both control either individual or groups of females for breeding purposed. The dolphins develop strong bonds with 1-2 different males, and all cooperate to form aggressively maintained “consortships” with females, and similarly, the chimpanzees cooperate in pairs and will “herd” individual females into groups. Studies have also been done to show that captive bottlenose dolphins and sexually dimorphic primates such as baboons and chimpanzees have even more patterns in common including “higher rates of male agonism, male dominance over females (even when physically smaller), and greater stability of dominance relationships among females (1).”
In conclusion, the article wraps up with a short discussion about the evolution of brain size comparisons in toothed whales and terrestrial mammals. Not many people appreciate or understand the vast difference in brain size among toothed whales and animals of the same size (2-3 fold for species of the same body size in some cases (1)). Some hypotheses for large brain evolution in terrestrial mammals include either the costs of maintaining large brains, or their benefits. And even though the parallels in social structure are captivating, the likelihood of equally “complex patterns of resource distribution, for example, may render these hypotheses as difficult to test in toothed whales as they have been in terrestrial mammals (1).” Research on odontocete behavior has been difficult in comparison to terrestrial mammal behavioral research for obvious reasons; however, I believe that we have only just begun to scrap the surface about these marine mammals. Even in this journal article from 1998 they realized that we may have a deeper connection to these creatures that we need to keep researching, and as the authors put it, “it is apparent that the effort is worthwhile; not only do we find remarkable convergence in a vastly different physical environment and ecosystem, we are also finding social phenomena which have no precedent on terra firma (1).”
References:
4.) Bottlenose Dolphin Picture. Photograph. Hitech-dolphin.com. Web. 27 Nov. 2011. .
5.) Sperm Whale. Photograph. The Encyclopedia of Science. Web. 27 Nov. 2011. .
Sorry, my references didn't show up too well in the post, the websites aren't on there for some reason. If you are interested in the website addresses for the pictures or article you can contact me at foxsar@onid.orst.edu
ReplyDeleteGreat article and information on terrestrial mammals and Whales. About the distinctive pair of "battle" teeth, since males develop these pair of teeth only and seem to live longer than the females, than over time have females decreased in number because males only have these teeth? Do females get attacked by other predators in the ocean more often and wouldn't they develop these teeth as well?
ReplyDeleteI seem to be very interested in this article. Seeing that males mature faster than females, would environment have an effect on the Baird's Beak Whales?
Yeah this article was very interesting to me as well, I have always wanted to work with animal behavior/social systems, so it was interesting to read about marine mammals in this context. In answer to your first question, it was only the Baird's beaked whale species that they said lived longer than the females, they did not say anything really about the lifespan of other beaked whale species. Also in Baird's beaked whales, BOTH males and females have these "battle" teeth, they did not discuss the reasons why in other species of beaked whales females do not posses these teeth, however I think that it is possible that the females of other beaked whale species have decreased over time because of the absence of these teeth.
ReplyDeleteIn answer to your second question, females (of other beaked whale species) may indeed get attacked more often by predators in the ocean since they do not have these teeth. However, the authors did not really address that the males used their teeth to fend off predators, they mainly discussed how they used them for male-male combat, so they might have had a completely different way of avoiding and/or fending off predators.
And environment could have an effect on Baird's beaked whales, for example if there was a confined feeding area where all the best fish hung out, and a large group of quickly maturing males and slowly maturing females, I can see the males most likely fighting over the group of fish, and possibly hurting and/or fatally wounding each other in the process. In this case the food environment would have a direct effect on the male Baird's beaked whales (the females may fight for the food too, but since they don't mature as fast they may not have that strong of instinct yet).
We should be careful about assigning the function of battle teeth here. They may be used in feeding, predator defense, or social interactions. I would be skeptical of females having shorter lifespans because of lacking these traits. If that were the case, then there would be selection for the traits to evolve in females. Since they are not there, and populations are usually not far from their natural selection optimum (and the fact that they carry all the genes necessary to make battle teeth, they're just turned off), then it is somewhat unlikely that females are maladapted. Also, I'm not sure I'm convinced that males live longer than females here as a general phenomenon. Very little is known about beaked whale's life history, and the 30 year difference that Sara mentions is in maximum lifespan observed in the wild from two recorded individuals, not differences in average lifespan for each sex, which probably are very poorly estimated.
ReplyDeleteAlso, make sure that when you say "females decrease over time" that what you mean is not evolutionary change. Even if females were 50% of the population, but only 1% survived to adulthood, the next generation would still be 50% females.
This was a great article with some very interesting points about evolution. I found the most interesting aspect of this article to be the weird similarities between such a wide range of species. It makes sense for the aquatic mammals to share some very key characteristics, however it is a bit strange that many of these traits would apply to large land mammals as well. Probably the most fascinating comparison in this post was between dolphins and chimpanzees in regards to foraging. Their environements seem to be be entirely different so this type of behavior doesn't make much sense. There are many animals in nature where the males are dominant over a few different females. Do you think some of the relationships found in this research are simply coincidental?
ReplyDeleteI love this article! First of all dolphins and aquatic mammals are some of the most intelligent species on earth despite the large brain size of terrestrial mammals. Marine mammals are also part of the tetrapods (four legged animals) as well as terrestrial mammals so the major difference is that marine mammals returned back to the water after going onto land. So it therefore makes sense that a lot of the behavioral patterns of both terrestrial and aquatic mammals are the same since they are both mammals, some just happen to live in water. Simply having a different environment doesn't mean you have abandon behaviors you've used before on land such as foraging for food. On the other hand adaptive mechanisms for reception in water are needed such echolocation and distinguish marine mammals from their terrestrial counterparts. So this leads me wonder, is it possible that due to open ocean limiting resources that it's the best reproductive strategy to stay together in groups or with specific individuals than to wander off and grow and mature on your own?
ReplyDeleteThis article has a lot of fascinating details about these organisms, but we should be careful not to infer causation. For example, a male keeping a group of females for reproductive access is pretty common in the natural world and so may have little baring on brain size and superior function that really seems to be the main topic of this article. Also, the battle teeth in the female porpoise may be a trait that was beneficial for the males, but not been able to diverge from developing in the female, and so have persisted. Much like super-popular males having nipples example in primates. (Annie Bollard)
ReplyDeleteThis article was very thought provoking. It was very interesting that these marine mammals have so many similarities with some terrestrial mammals, even though they branched off from each other quite some time ago. I feel like it may be incorrect to say that these similarities could be present just because of phylogenetic constraints. There are so many mammals that do not share these characteristics that it seems highly unlikely. Hippopotami are supposed to be sister taxa to the clade that contain whales and dolphins, and they don’t share these same similarities. I am wondering if the genes that code for increase in intelligence are somehow correlated to the social traits that these animals have. Higher intelligence could correlate with improved memory, which could impact family and social relations. Higher intelligence may also be correlated with readiness to cooperate in groups, which may allow for the cooperative care of vulnerable infants in sperm whales and infants. It makes me think back to the domestic fox example where selecting for docile behavior also brought another suite of traits along for the ride. If the shared traits between intelligent marine and terrestrial mammals do have something to do with phylogenetic constraints, could these traits be possible in any mammals if they evolved a bigger brain (i.e. gain a higher intelligence)? Or maybe this is all just convergent evolution and it is just coincidence. It would be interesting to do some tests and compare the brains of whales/dolphins and chimps/elephants.
ReplyDeleteI really enjoyed reading this post. I work part-time at the Oregon Coast Aquarium in the education department so this article has information I can teach to my groups (We have a beaked whale skeleton at the aquarium). I found it interesting that they are proposing that the Baird’s beaked whale males provide a significant amount of parental care. I agree with Annie in her post above... We need to be really careful about inferring causation when we consider what is proposed in this article regarding battle teeth as well as why they disperse or stay together. Is the increased amount of brain, or the higher intelligence that we observe in these animals what has them group together in social groups or is it just out of necessity for food, reproduction, and safety in the vast expanse of the ocean?
ReplyDeleteI am interested in the difference in eventual dispersal of either males or females away from a population. Initially I thought that maybe these sea mammals stay in closer proximity because the cost associated with trying to fond mates in the vastness of the open ocean may be greater than the cost of closely related individuals breeding. However, I as kept reading and thinking my thoughts changed a bit. Whether on land or in sea, large brained mammals have life histories that involve less dispersal. Perhaps these similarities are because with increased brain size come increased cognition and abilities to recognize and remember. If the cost of inbreeding can be avoided without the cost of dispersal than remaining near close relatives would increase fitness. Humans often live in very close proximity with very close relatives. However, we are able to recognize close relatives and avoid breeding with them.
ReplyDeleteIn response to some of the above posts, yes I realize that we need to be careful when inferring causation, however, it was merely the authors of the article that seemed to do that, I did not mean to come across saying that in any way. I think the authors were just trying to come up with some interesting hypotheses as to why toothed whales and terrestrial mammals are similar, they weren't trying to say, "this is the truth about why these animals evolved in this particular way," because they really couldn't be 100% sure.
ReplyDeleteI found this article very fascinating and enjoyable because I am marine biology major, and I also find research with marine mammals interesting. The thing that surprised me the most was that chimpanzees and bottlenose dolphins were described as having a very similar social structure. It would be interesting to see if there is any additional research into this subject. For example: to see if this would be an example of convergence through cultural evolution.
ReplyDelete-written by Karina Belica
It is interesting to read that species with as little in common as large brain size can share so many similarities in behavior. I would be interested in learning more about the cause and effects of large brain size and the differences/similarities between species with this in common.
ReplyDeleteThe similarity between the social structures of dolphins and chimpanzees was especially interesting to me. The fact that they both sleep in larger groups but forage in smaller groups makes me wonder how much of the similarities between the species is actually due to genetic effects and not environmental constraints. Even though the environments that either species lives in are incredibly different, the fact that their primary food sources are both "patchy" in dispersal makes me wonder if commonality in brain size is only a superficial contributor to behavior.
Additionally, it would be interesting to see a comparison of species with parallel behavior that do not share similarly large brain size. What other species with comparatively small brains show the same behaviors such as late male maturity, matrilineal grouping, and care of offspring by the male of the species? It is intriguing to read about the correlation between large brain size and behavior but makes me curious to learn of other common influences these species experience that may also be working to shape their behavior.