Abstract
The differential allocation hypothesis predicts that reproductive investment will be influenced by mate attractiveness, given a cost to reproduction and a tradeoff between current and future reproduction. We tested the differential allocation hypothesis in the swordtail fish Xiphophorus multilineatus, where males have genetically influenced (patroclinous inheritance) alternative mating tactics (ARTs) maintained by a tradeoff between being more attractive to females (mature later as larger courting males) and a higher probability of reaching sexual maturity (mature earlier as smaller sneaker males). Males in X. multilineatus do not provide parental care or other resources to the offspring. Allelic variation and copy number of the Mc4R gene on the Y-chromosome influences the size differences between males, however there is no variation in this gene on the X-chromosome. Therefore, to determine if mothers invested more in offspring of the larger courter males, we examined age to sexual maturity for daughters. We confirmed a tradeoff between number of offspring and female offspring’s age to sexual maturity, corroborating that there is a cost to reproduction. In addition, the ART of their fathers significantly influenced the age at which daughters reached sexual maturity, suggesting increased maternal investment to daughters of courter males. The differential allocation we detected was influenced by how long the wild-caught mother had been in the laboratory, as there was a brood order by father genotype (ART) interaction. These results suggest that females can adjust their reproductive investment strategy, and that differential allocation is context specific. We hypothesize that one of two aspects of laboratory conditions produced this shift: increased female condition due to higher quality diet, and/or assessment of future mating opportunities due to isolation from males.
Highlights
According to life history theory, natural selection favors behaviors that maximize lifetime reproductive success based on several key tradeoffs
Provided that mothers can adjust the investment devoted to each offspring and that females have reliable cues predicting future environmental conditions, several factors have been proposed to determine facultative differential allocation by mothers [4,5]: 1) if larger females have more resources to allocate to reproduction, they may produce larger broods and/or larger offspring [6,7,8]; 2) if females can assess their likelihood of future reproduction, they should invest heavily in their last reproductive events; 3) females are predicted to adjust their investment in offspring depending on the attractiveness of their mate, as long as there is a cost to reproduction, a tradeoff between current and future reproductive success and evidence that mating with high quality mates increases female fitness [9,10,11,12]
We examined factors influencing variation in brood size and age at maturity with two Generalized Linear Models (GzLM) that included the independent variables, the weighting scheme and its respective covariables
Summary
According to life history theory, natural selection favors behaviors that maximize lifetime reproductive success based on several key tradeoffs. Such tradeoffs can be grouped in two main categories: between present and future reproduction (e.g. reproduction vs growth, survival etc.), and within present reproduction, between quantity and quality of offspring (number of offspring vs size, age at maturity, etc.) [1]. To better understand selection for facultative adjustment of reproductive investment as well as its evolutionary consequences, we will need more empirical studies that can unite measures of mate preference with the benefits of the preferences [10,15,17,20]
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