SFB-TRR 212

Male sexual competition as a social niche dimension: adaptive niche conformance and its proximate mechanisms in a species with male parental care

How do males of biparental species trade off securing fertilisations versus parental investment in response to the extent of sexual competition with which they are individually confronted? The overall goal of our project is to answer this open question in order to understand how individual variation in sexual competition generates individual variation, and covariation, in both competitive traits and parenting behaviour. Females of most animal species mate with more than one male resulting in sperm competition. Here, we consider variation in sperm competition risk (SCR, the probability that at least one rival ejaculate is present) as one of the many dimensions of the social niche to which individual males are exposed. This social niche dimension is one of paramount significance given sperm competition represents a nearly ubiquitous selection pressure on the male sex in animals, including most socially monogamous species. Thus, how well a male individual manages to achieve a match between the level of SCR encountered and his integrated reproductive phenotype, defined here to include both competitive and parental traits, will directly affect his reproductive success and hence fitness.

Here we propose to investigate how males of a well-characterised model system, the Zebra Finch Taeniopygia guttata, plastically adjust their phenotype in order to conform to their social niche as defined along an axis of experimentally induced variation in SCR. To fully capture conformance of the integrated male reproductive phenotype to the level of SCR, we consider it essential to simultaneously assess responses in both pre- and post-copulatory competitiveness as well as in male parental care. Furthermore, we aim at integrating functional and mechanistic levels of explanation by not only studying the plasticity of key phenotypic traits and its adaptive significance, but also the underlying endocrinological and transcriptomic mechanisms.

To test the hypothesis that males conform to their individualised social niche as defined by SCR, we will

1. investigate to what extent males tune competitive behaviours and ejaculate traits in response to experimentally induced variation in SCR;
2. identify the underlying endocrinological and transcriptomic mechanisms which are mediating the predicted plastic responses;
3. test for the adaptive significance of plasticity in sexual behaviours and ejaculate traits under a niche match/mismatch paradigm; and
4. assess the downstream effects of competitive adjustment to SCR on male parental care.

Through the comprehensive assessment of conformance of the integrated male reproductive phenotype to its individualised social niche within a single experimental framework our project will break new ground. Importantly, the inclusion of downstream effects of male competitive investment on male parental care will contribute significantly to our understanding of the fundamental trade-off between fertilising more eggs versus providing more parental care per fertilised egg. More generally, our project will help in understanding how male conformance to individualised social niches generates individual variation in both competitive traits and parental behaviour, and elucidate how this variation is modulated through the underlying physiological and molecular mechanisms. It therefore links directly to major goals of the CRC NC3: demonstrating that individualised niche-phenotype matches are crucial for individual fitness, and thus for adaptive processes, and that the individualised responses to achieve that match are mirrored closely by the molecular and physiological machinery enabling these.