Male-male amplexus between two amphibian families

The amplexus between two different anuran males is observed very rarely. Therefore, here we provide the first documented observation of a long-lasting male-male amplexus between Bombina bombina (Bombinatoridae) and Hyla arborea (Hylidae) together with an overview of the data published in literature. The observed mating pattern is reported from Southern Moravia, the Czech Republic. The possible reasons for its occurrence during the mass breeding season are discussed.

Assortative mating, sexual selection and their consequences for gene flow in Littorina

When divergent populations are connected by gene flow, the establishment of complete reproductive isolation usually requires the joint action of multiple barrier effects. One example where multiple barrier effects are coupled consists of a single trait that is under divergent natural selection and also mediates assortative mating. Such multiple-effect traits can strongly reduce gene flow. However, there are few cases where patterns of assortative mating have been described quantitatively and their impact on gene flow has been determined. Two ecotypes of the coastal marine snail, Littorina saxatilis, occur in North Atlantic rocky-shore habitats dominated by either crab predation or wave action. There is evidence for divergent natural selection acting on size, and size-assortative mating has previously been documented. Here, we analyze the mating pattern in L. saxatilis with respect to size in intensively-sampled transects across boundaries between the habitats. We show that the mating pattern is mostly conserved between ecotypes and that it generates both assortment and directional sexual selection for small male size. Using simulations, we show that the mating pattern can contribute to reproductive isolation between ecotypes but the barrier to gene flow is likely strengthened more by sexual selection than by assortment.

Mating pattern, female reproduction and sexual size dimorphism in a narrow-mouthed frog (Microhyla fissipes)

The difference in body size and/or shape between males and females, called sexual size dimorphism, is widely accepted as the evolutionary consequence of the difference between reproductive roles. To study the mating pattern, female reproduction and sexual size dimorphism in a population of Microhyla fissipes, amplexus pairs were collected, and the snout-vent length of males and females, female reproductive traits and fertilization rate were measured. If the body size of amplexed females is larger than that of amplectant males, this is referred to as a female-larger pair, a phenomenon that was often observed for M. fissipes in this study. Interestingly, snout-vent length of males in male-larger pairs was greater than that in female-larger pairs, however the post-spawning body mass, clutch size, egg dry mass and clutch dry mass did not differ between both types of pairs. Snout-vent length of males was positively related to that of females in each amplexus pair. After accounting for the snout-vent lengths of females, we showed that snout-vent lengths of males in male-larger pairs were greater than those of females in female-larger pairs. The snout-vent length ratio of males and females was not related to fertilization rate in each amplexus pair. The mean fertilization rate was not different between both amplexus pairs. These results suggest that (1) M. fissipes displays female-biased sexual size dimorphism and has two amplexus types with size-assortative mating; (2) the snout-vent length ratio of males and females in each amplexus type was consistent with the inverse of Rensch’s rule, and was driven by the combined effect of sexual selection and fecundity selection; (3) females with a larger body size were preferred by males due to their higher fecundity, while the body size of males was not important for fertilization success.

Evolution favors aging in populations with assortative mating and strong pathogen pressure

Since at first sight aging seems to be omnipresent, many authors to this very day regard it as an inevitable consequence of the laws of physics. However, studies published in the past two decades have conclusively shown that a number of organisms do not age, or at least do not age on a scale comparable with other aging organisms. This disparity leads us to question why aging evolved in some organisms and not in others. We thus present a mathematical model which simulates evolution in a sexually reproducing population composed of aging and non-aging individuals. We have observed that aging individuals may outcompete non-aging individuals if they have a higher starting fertility or if the main mating pattern in the population is assortative mating. Furthermore, stronger pathogen pressure was found to help the aging phenotype when compared to the non-aging phenotype. Last but not least, the aging phenotype was found to more easily outcompete the non-aging one or to resist the dominance of the latter for a longer period of time in populations composed of dimorphic sexually reproducing individuals compared to populations of hermaphrodites. Our findings are consistent with both classical evolutionary theories of aging and with evolutionary theories of aging which assume the existence of an aging program. They can thus potentially work as a bridge between these two opposing views, suggesting that the truth in fact lies somewhere in between.Significance StatementThis study presents the first mathematical model which simulates the evolution of aging in a population of sexually reproducing organisms. Our model shows that aging individuals may outcompete non-aging individuals in several scenarios known to occur in nature. Our work thus provides important insight into the question why aging has evolved in most, but not all, organisms.

Occurrence of Interspecific Mating between Two Species of Danaus Kluk, 1780 (Lepidoptera: Nymphalidae) in Nature

Mating across species occurs rarely in nature, which contends prevalent idea of biological species concept. Throughout species range, mating pattern varies and reproductive barriers are also not fixed among different species. In this study, two instances of interspecific mating between two widely common Nymphalid Tiger butterflies (Danaus Kluk, 1780) in Indian region are reported. Observations imply lack of absolute reproductive barriers, where possible interplay exists among prezygotic and postzygotic isolating factors compensating each other in order to restrain interspecific hybridization.

MateSim: Monte Carlo simulation for the generation of mating tables

In species with sexual reproduction, the mating pattern is a meaningful element for understanding evolutionary and speciation processes. Given a mating pool where individuals can encounter each other randomly, the individual mating preferences would define the mating frequencies in the population. However, in every mating process we can distinguish two different steps. First, the encounter between partners. Second, the actual mating once the encounter has occurred. Yet, we cannot always assume that the observed population patterns accurately reflect the individual’s preferences. In some scenarios the individuals may have difficulties to achieve their preferred matings, such as in monogamous species with low population size, where the mating process is similar to a sampling without replacement. In the latter, the encounter process will introduce some noise that may disconnect the individual preferences from the obtained mating pattern. Actually, the difference between the mating pattern observed in a population and the mating preferences of the individuals have been shown by different modeling scenarios.Here I present a program that simulates the mating process for both discrete and continuous traits, under different encounter models and individual preferences, including effects as time dependence and aging. The utility of the software is demonstrated by replicating and extending, a recent study that showed how patterns of positive assortative mating, or marriage in human societies, may arise from non-assortative individual preferences. The previous result is confirmed and is shown to be caused by the marriage among the “ugliest” and oldest individuals, who after many attempts were finally able to mate among themselves. In fact, I show that the assortative pattern vanishes if an aging process prevents these individuals from mating altogether. The software MateSim is available jointly with the user’s manual, at http://acraaj.webs.uvigo.es/MateSim/matesim.htm