Mating in instable habitats and polyandry in frogs : the role of sexual conflict…
Since their appearance at Devonian, Amphibians diverged in numerous species differing in their genetic pool. Within a species distinct populations also exhibit genetic variability. This differentiation (polymorphism) may either lead to speciation (new species birth) or favour local adaptation. Our goals deal with evolutionary ecology in numerous topics:
Population structure and gene flow
Agile frogs Rana dalmatina are terrestrial Anuran inhabiting natural meadows and woods
Population structure and gene flow can be influenced by habitat distribution. Agile frogs gathered in spawning ponds from February to the beginning of April and chorused over a two week time. During breeding time, males often predominated in populations but were intensively preyed upon by predators especially Polecats. The predation reducing population exchanges may result in differentiation among frog populations.
Sexual conflict and Polyandry in Agile frogs
Amplexus in Agile frog
Questions: Understanding why females mate multiply is a major issue in evolutionary ecology. Does the operational sex ratio influence reproductive success and offspring survival ?
Reproductive success of agile frog (Rana dalmatina) was surveyed at breeding sites. Variations in the adult sex ratio and operational sex ratio did affect reproductive success. Asynchronous arrival at breeding sites resulted in a male-biased operational sex ratio (OSR). The OSR was more strongly male-biased at the beginning and at the end of the breeding period when the number of satellite males increased.
In Rana dalmatina, the increase in male biased operational sex ratio and in male abundance results in a strong emergence of alternative male mating behaviour in the form of searching, and sneaking. As a consequence, females are coerced into mating with multiple males, which in turn increases the level of conflict between the sexes (sexual conflict).
All females mated at least once, but genetic evidence for multiple paternity within clutches occurred at the beginning and the end of the breeding period. The influence of asynchronous arrival and biased sex ratio entailed reduced variance and bet-hedging. The conflict of interest between the two sexes was the focus for the alteration in reproductive success as revealed by the number of emergent froglets.
Predation influences monoandry in frogs !
Furthermore, predation by polecats Mustela putorius was found to influence sex ratio, male abundance and sexual conflict in frog mating system, restricting the opportunity for multiple mating.
Polecat predation upon frog
Such an exceptional interaction, resulting in sexual system changes, was demonstrated for the first time in polecat-frog (predator-prey) co-existence strategies.
Road effect and Amphibian conservation
In populations of Agile frog, the observed heterozygosity was significantly lower than expected in all cases, and the strong mortality gives new evidence of a depression in small populations exposed to roads. It especially occurred in ponds located near an highway rather than in undisturbed populations. Our results argue for a “road effect zone” and emphasize the importance of management measures such as amphibian tunnels for conservation.
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