New study finds that male lizards use different tactics to win the ladies - via Herp Digest

October 21st, 2013 (Phys.org) —New collaborative research conducted by Macquarie University and the Australian National University on a common Australian lizard, the Eastern Water Skink, has revealed that sexual selection, the process whereby certain individuals gain a reproductive advantage, likely promotes the evolution of 'floater' and 'territorial' behavioural reproductive tactics in males.

The researchers studied six marked populations of the Eastern Water Skink in large naturalistic outdoor enclosures. They followed the movements and behaviour of males during the breeding season, and used genetic paternity testing to determine reproductive fitness.

"Ultimately, we were interested in what behavioural traits make a successful male lizard" said lead researcher Daniel Noble.

"As it turns out, large males that adopt either a territorial-like tactic (where they defend a fixed area), or a 'floater' or 'sneaker'- like tactic (with no defense of a particular space, but who move over a wider area), father the most offspring and therefore have the highest fitness."

Alternative reproductive tactics (ARTs) have been studied in a wide range of species. However, few studies document ARTs in species where there are no distinguishing features separating males from each other. This study demonstrates that ARTs can be driven by behaviour alone.

Noble explains "Males adopting ARTs are often distinct from one another in terms of body size, colouration, or the presence and size of armaments such as horns. We know very little about ARTs in nondescript species.

"What makes these results particularly interesting is that we simply quantified behavioural variation to test whether there was evidence of disruptive selection on trait combinations predicted to be associated with ARTs in water skinks.

"In many systems, we cannot take this approach because polymorphic species (that is, males with different coloration) lack intermediate phenotypes. Our results have important implications for understanding the early evolution of ARTs because they suggest selection starts by acting on more labile behavioural traits, which allow males to gain access to mating opportunities through different mechanisms."

The authors have documented a rare case of ARTs evolving through selection on suites of male behaviours. This cryptic system may be more common than currently understood, and underscores the importance of behaviour as an ART in its own right.

The research paper has been published in full online in the American Naturalist.

More information: Daniel, W. et al. Behavioral and Morphological Traits Interact to Promote the Evolution of Alternative Reproductive Tactics in a Lizard (2013), The American Naturalist. www.jstor.org/stable/10.1086/673535

Provided by Macquarie University

Size Does Matter in Sexual Selection, at Least Among Beetles

ScienceDaily (Oct. 25, 2012) — A new collaborative project among researchers from Uppsala University in Sweden and the University of Cincinnati has, for the first time, demonstrated experimentally the evolutionary force behind the rapid evolution of male genitals, focusing on a species of seed beetle.

 This mechanism is revealed in a study published October 25 in the scientific journal Current Biology. The experiments leading to this paper involved a species of seed beetle known as Callosobruchus maculatus. Mating among these beetles involves several males engaging in copulation with individual females.

"When a female mates with several males, the males compete over the fertilization of her eggs," said Michal Polak, associate professor of biological sciences at the University of Cincinnati, one of the co-authors. "Because females mate with multiple males, the function of the male copulatory organ may determine which of the males will fertilize most of her eggs. Our results show that the morphology of the male genitalia affects his fertilization success in these beetles."

The competition to produce offspring is the driving force of evolution. Competition among males occurring after insemination may be an important evolutionary force that has led to the evolution of a diversity of shapes and sizes of male sexual organs, the co-authors assert. This competition among males has generated a great biological diversity that they believe can directly contribute to the formation of new species.

Continued:  http://www.sciencedaily.com/releases/2012/10/121025130924.htm

Less Is More, for Female Cowbirds: Findings Contradict Sexual Selection Theory

ScienceDaily (May 4, 2012) — More modest male displays attract the females when it comes to brown-headed cowbirds, contrary to sexual selection theory, according to UC Santa Barbara researchers Adrian O'Loghlen and Stephen Rothstein.

Their findings are published May 2 in the open access journal PLoS ONE.

While sexual selection theory predicts that females should find more flamboyant displays the most sexually attractive, the opposite holds true for brown-headed cowbirds, a small songbird common in North America. Using audiovisual recordings of displaying males shown to captive females, the scientists found that the less intense the wing spreading, feather puffing, and bowing were during a display, the more sexually interested the female would be.

"Although cowbirds have been studied for years, it hadn't really been noticed that displays directed at females were different in intensity than those directed at other males," said O'Loghlen, a research scientist in the Department of Ecology, Evolution and Marine Biology. However, technical advances in the area of audiovisual recordings made it possible for the researchers to investigate the brown-headed cowbirds's display behaviors in greater depth. O'Loghlen and Rothstein, a professor of Zoology, are the first to use AV technology to study the sexual responses of female songbirds to male displays.

Continued:http://www.sciencedaily.com/releases/2012/05/120504110558.htm