UC San Diego

A number of factors influence the expression of an individual's sexually selected traits. These include genes, environmental factors, parental effects, and the individual's condition. Parental effects can also affect offspring condition. This dissertation considers factors influencing offspring condition, and how genes and parental effects contribute to the expression of the sexually selected wing-bar Phylloscopus humei, a monomorphic species. Males use their wing-bars in interactions determining territory size, but other forms of selection on the wing-bar have not been identified. I studied a breeding population of P. humei in the Manali Sanctuary, Manali, Himachal Pradesh, India breeding along an elevational gradient. In Chapter I, I use this elevational gradient to gain insight into factors that might explain nestling condition. The hatch date of nestlings has been commonly found to be important in their survival and fitness, with earlier-hatching birds faring better than those hatching later in the season. It is unclear whether this effect results as a direct consequence of the actual date of hatching or via parental transmission of fitness to offspring (with higher condition birds breeding earlier). I found that chicks hatching at higher elevations did so later in the season and were in poorer condition than were chicks hatching earlier at low elevation. There was no detectable compensation for late breeding at higher elevations, suggesting that parents pass their condition to their offspring. The following two chapters examine possible influences on monomorphism, focusing on the wing-bar. In Chapter II, I assess extra-pair paternity in the species and how it might affect selection on the wing-bar. Using newly isolated microsatellite primers, I assessed parentage in this population as well as in a handful of families sampled in Naran, Pakistan. The rate of extra- pair paternity was high and similar across years and in two populations--35% overall in Manali and 32% in Naran. There was no association of wing-bar size, either in adult males or in offspring, with extra-pair paternity, and it appears that the high levels of extra-pair paternity may be a result of male harassment of females owing to the high density and breeding synchrony of the species. Chapter III considers another possible influence on monomorphism in P. humei--the inheritance of wing-bar size. Using parent-offspring regressions across sexes, this chapter determines that the wing-bar's presence in females is a result of a genetic correlation between the sexes. This genetic correlation is sufficiently strong that dimorphism is not expected to develop. However, there is a difference in the magnitude of heritability of wing- bar size between mothers and their sons and daughters. This may be the result of a sex-specific maternal effect acting on inheritance of the size of the wing-bar. Additionally, based on observations of female behavior, it is likely that the wing-bar may serve them a function, though it has not yet been determined