Now that a general evolutionary explanation for monogamy has been given in the previous post, I will continue by comparing some of the mating strategies and styles of parental care seen across different classes of animals including deeper examinations of certain species of aves, amphibians, and mammals.
Remember however, that social monogamy doesn’t predict genetic monogamy in animals. In other words, most animals continue to have extra-pair paternity within their pair-bonds (in simple English, ‘cheating’). The amount of extra-pair copulations is subject to modulation by factors such as the length of an animal’s breeding season, the amount of parental care the male (rarely female) shows and the amount of sexually receptive females (rarely males) are present (Huck Maren, Fernandez-Duque Eduardo, Babb Paul, & Schurr Theodore, 2014). Therefore, different animals who may be considered socially monogamous can have wildly different rates of genetic monogamy in their offspring.
The red-backed salamander, an amphibian that has been seen to demonstrate socially monogamous behavior, was assessed by researchers for their rates of genetic monogamy and parental care. Results indicated that not one of the of the broods with biparental care analyzed (n=16) were genetically monogamous (Liebgold, Cabe, Jaeger, & Leberg, 2006). To rephrase, in all the broods, not one group had all full siblings. Eighty-five percent of broods had multiple sires, most with two or three (Liebgold et al., 2006). In this species, it seems a longer breeding season may give more opportunities for extra-pair relations. This may seem counter intuitive, as one may think that with less time to reproduce during the year would be correlated with more instances of extra-pair relations. However, one thing that remains intuitive in this species is the amount of biparental care exhibited based on supposed certainty of paternity. In this study particularly, only twenty-five percent of broods had biparental care (Liebgold et al., 2006). Perhaps if the rate of extra-pair relations decreased, the rate of biparental care in this species would increase.
Since monogamous behavior evolved several times in vastly different creatures, it is my personal belief that there is not just one theory that explains why monogamy appears in any given instance. However, one article focused on a species of poison frog (ranitomeya imitator) and concluded that the biparental care hypothesis was the most reasonable explanation for the appearance of monogamy in its case (Tumulty, Morales, & Summers, 2014). These researchers defined biparental care by responsibilities such as egg attendance, tadpole transport, and feeding of tadpole offspring. The researchers tested their support for the biparental care hypothesis in these poison frogs by removing the male from the pair-bond and recording the effects of the removal on the tadpole offspring. Compared to tadpoles with a present father-figure, those tadpoles without had lower growth rates and survival rates (Tumulty et al., 2014). Although the data partly supported the biparental care hypothesis, I do not think that this study proves that biparental care and the resulting increase in offspring survivability cause monogamy. This study and others alike it (even those that support different ideas for the evolution of monogamy) often fail to make an argument for the causes versus the effects of monogamy. It’s difficult to accept the premise that biparental care was the first and causal step in the evolution of monogamy when other factors such as limited number of females seem to logically precede any modification in parental care behaviors.
In the Volatinia jacarina, a tropical bird species, it seems that the behavior of the males influence the rate of extra-pair fertilizations (Carvalho, Macedo, & Graves, 2006). The more successful males display behavior that is likely correlated to health and fitness, and they ultimately deal with less extra-pair copulations from their female partners. In this article, the authors propose the opposite of Liebgold et al., (2006) and state that a short breeding season may increase the number of extra-pair fertilizations in males that display unsuccessful behavior (Carvalho et al., 2006). Tropical birds however, seem to be an underrepresented subset of animal in the research of monogamy, so more research is necessary for a greater understanding of their sexual behavior. In Ara ararauna, another species of aves, genetic monogamy is much more common (in this study over 90%), as is male parental care, thus strengthening the evidence for the association (Caparroz, Miyaki, & Baker, 2011).
In primates, some would argue that infanticide leads to social monogamy (Opie, Atkinson, Dunbar, & Shultz, 2013). Although there were letters posted on the website along with the article addressing some people’s strong disagreement, I do not believe it is unreasonable that in at least some species, infanticide may have been the leading cause of the evolution of social monogamy, and that the other behaviors that come with monogamy are merely effects of the prevalence of infanticide.
- Social monogamy does not equal genetic monogamy.
- Different species have vastly different rates of extra-pair copulation behavior, and these differences are modulated by factors like length of breeding season, and can affect things such as male (rarely female) parental care.
Caparroz, R., Miyaki, C. Y., & Baker, A. J. (2011). Genetic evaluation of the mating system in the blue-and-yellow macaw (Ara ararauna, Aves, Psittacidae) by DNA fingerprinting. Genetics and Molecular Biology, 34(1), 161–164. https://doi.org/10.1590/S1415-47572010005000112
Carvalho, C. B. V., Macedo, R. H., & Graves, J. A. (2006). Breeding Strategies of a Socially Monogamous Neotropical Passerine: Extra-Pair Fertilizations, Behavior, and Morphology. The Condor: Ornithological Applications, 108(3), 579–590. https://doi.org/10.1650/0010-5422(2006)108[579:BSOASM]2.0.CO;2
Huck Maren, Fernandez-Duque Eduardo, Babb Paul, & Schurr Theodore. (2014). Correlates of genetic monogamy in socially monogamous mammals: insights from Azara’s owl monkeys. Proceedings of the Royal Society B: Biological Sciences, 281(1782), 20140195. https://doi.org/10.1098/rspb.2014.0195
Liebgold, E., Cabe, P., Jaeger, R., & Leberg, P. (2006). Multiple paternity in a salamander with socially monogamous behaviour. Molecular Ecology, 15, 4153–4160. https://doi.org/10.1111/j.1365-294X.2006.03076.x
Opie, C., Atkinson, Q. D., Dunbar, R. I. M., & Shultz, S. (2013). Male infanticide leads to social monogamy in primates. Proceedings of the National Academy of Sciences, 110(33), 13328–13332. https://doi.org/10.1073/pnas.1307903110
Tumulty, J., Morales, V., & Summers, K. (2014). The biparental care hypothesis for the evolution of monogamy: experimental evidence in an amphibian. Behavioral Ecology, 25(2), 262–270. https://doi.org/10.1093/beheco/art116