Impact of adult male food limitation and male seasonal phenotype on female fitness, in the African butterfly Bicyclus anynana.

Details

Supervisors

Nieberding, Caroline M.

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie

Abstract

Climate change is not a new topic in biology ; its impacts on plants and animals has been studied for more than 100 years. Climate change is characterized by an increase of the temperature mean and variance, an increase of the occurrence of extreme weather events and an increased environmental stochasticity. One expectation may be that phenotypically plastic species be especially vulnerable to climate change as the environmental cues on which they rely to produce the phenotypes adapted to the coming season will not constitute reliable predictors for seasonal progression anymore, leading to phenotype-environment mismatch. Moreover, climate change is expected to alter species phenologies and interactions across trophic levels (predator-prey and plant-insects interactions), leading to increased food limitation and starvation risks. The case studied here is the polyphenic tropical butterfly Bicyclus anynana, which has evolved a temperature-induced seasonal polyphenism in order to fit the different ecological constraints of each season. It displays a wet (WS), an intermediate (IS) and a dry (DS) season phenotype. Some evidence of climate-change induced maladaptation were already brought to light for this species. For instance, it was shown that B. anynana individuals developing under the 2100 climatic scenarios displayed the wet season phenotype instead of the dry season phenotype at the onset of the harsh dry season. It was also shown that females that were shortly exposed to either male seasonal form during sexual maturation prior to mating experiments shifted their innate and adaptive sexual preference for dry season males and learned to prefer the intermediate season phenotype. This is considered maladaptive as the dry season phenotype was shown to confer higher longevity and fecundity to the females. Moreover, several studies have shown how adverse environmental conditions such as food stress experienced during juvenile and adult stages were major factors affecting important life-history traits, behavior and reproductive capacity in B. anynana. This master thesis aimed at providing complementary information on how climate-change driven alterations in the expression of seasonal phenotypes (1) and in (2) food availability could affect B. anynana species’ reproduction and probability of survival. In order to do so, we studied the impact of both male seasonal phenotype (WS vs. IS vs. DS) and food restriction applied to males on female fitness (using female longevity, fecundity and fertility as fitness proxies). Our results showed that, for each male season, male feeding treatment did not have an impact on any of the female fitness proxies. Based on those results, we could argue that B. anynana species’ survival might not be too heavily affected by climate change-induced food scarcity. Moreover, we found out that male seasonal phenotype did not have an impact on female longevity and fecundity but that it did have an impact on female fertility (WS males conferred higher fertility chances than DS males, no matter their feeding treatment). Based on those results, we could argue that the predicted display of the wet season form at the onset of the dry season due to rising temperatures could rather be a positive thing as WS males seem to confer higher fitness to females. However, it is important to note that our results have to be taken with a pinch of salt and do not allow us to draw trustworthy conclusions because we made an important mistake in our experimental protocol.