Feature Paper: Bigger is Better











In linking to the article on Brian Langerhans’ Bahamas research last week, I
realized I haven’t linked up to our “bigger is better” paper.

Mosquitofish (pictured above), unlike most fishes, have internal fertilization.  They use a modified anal fin, called a gonopodium, to deposit sperm in females.  And females may actually pay attention to the size of the gonopodium.  To test this, we used video images of males of the same size, with one having his gonopodium digitally altered to appear smaller.  The results were clear ……












So why don’t all males have big units?  The trade-off is that with a larger gonopodium, burst swimming speed is lower and thus large gonopodium males are more susceptible to fish predators.  So bigger is better, as long as there is nothing around to eat you.  Here is the full article summary…..

Male genitalia may experience more rapid, divergent evolution than any other animal character, but why? Research during the past several decades has culminated in the view that genital diversification primarily results from postmating sexual selection (e.g., sperm competition or cryptic female choice). However, the potential roles of premating sexual selection (e.g., mate choice) and natural selection have received little attention. We examined the possible importance of these mechanisms by investigating divergence in male genitalia among populations differing in predator regime for two species of live-bearing fish (Gambusia affinis in Texas and Gambusia hubbsi in The Bahamas). When controlled for body size, males exhibited a larger gonopodium (sperm-transfer organ) in predator-free environments than in predatory environments, a trend that persisted across space (multiple populations), time (multiple years), and species. By conducting laboratory experiments with G. affinis, we found that premating sexual selection seems to favor larger male genitalia (females exhibited mating preference for males having larger gonopodia), but natural selection in the presence of predatory fishes seems to favor reduced genital size (larger gonopodium size was associated with reduced burst-swimming performance, an important antipredator behavior). Although postmating sexual selection is widely presumed to be the most important mechanism driving genital diversification, these findings suggest that alternative mechanisms, particularly for organisms that cannot retract their genitalia, may also prove important.


By | 2017-12-01T14:04:46-05:00 August 27th, 2012|Categories: Blue Holes, Fish, Mangroves and Creeks|0 Comments

About the Author:

Craig Layman
My lab’s interdisciplinary pursuits provide for a multi-faceted understanding of environmental change in the coastal realm. We are ecologists, asking questions that span population, community, ecosystem and evolutionary sub-disciplines. We often use a food web based perspective, exploring top-down (e.g., predation) and bottom-up (e.g., nutrient excretion) mechanisms by which animals affect ecosystem processes. All of our efforts are framed within a broader outreach framework, directly integrating science and education, using approaches such as this website.

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