The quantitative genetic basis of offspring solicitation and parental response in a passerine bird with biparental care

Abstract

The coevolution of parental investment and offspring solicitation is driven by partly different evolutionary interests of genes expressed in parents and their offspring. In species with biparental care, the outcome of this conflict may be influenced by the sexual conflict over parental investment. Models for the resolution of such family conflicts have made so far untested assumptions about genetic variation and covariation in the parental resource provisioning response and the level of offspring solicitation. Using a combination of cross-fostering and begging playback experiments, we show that, in the great tit (Parus major), (i) the begging call intensity of nestlings depends on their common origin, suggesting genetic variation for this begging display, (ii) only mothers respond to begging calls by increased food provisioning, and (iii) the size of the parental response is positively related to the begging call intensity of nestlings in the maternal but not paternal line. This study indicates that genetic covariation, its differential expression in the maternal and paternal lines and/or early environmental and parental effects need to be taken into account when predicting the phenotypic outcome of the conflict over investment between genes expressed in each parent and the offspring.

The quantitative genetics of sex differences in parenting

“…There is a growing interest in the potential evolution of genetic correlations between parental provisioning and offspring solicitation as a sign of parent-offspring coadaptation (32,34). Studies have now demonstrated both positive (19,21,24) and negative (22,26) genetic correlations between female parents and their offspring. The only study to test for coadaptation between male parents and their offspring found no correlation between male care and offspring begging, despite a positive correlation between female care and offspring solicitation (21).…”

“…For example, we predict that asymmetries in the reproductive strategies of males and females, which result in sexspecific genetic variation in parental responses to offspring solicitation (28), will also reflect sex differences in patterns of genetic covariation. Preliminary evidence that this may well be the case comes from studies on several species of birds demonstrating differences between the sexes in the repeatability of provisioning (13,29) and a study of great tits (Parus major) reporting a genetic correlation between parental response and offspring begging (21). It now would be valuable to test whether males and females in these species differ with respect to genetic correlations between different parental behaviors and whether these differences match any behavioral specializations in parental care.…”

“…Studies have now demonstrated both positive (19,21,24) and negative (22,26) genetic correlations between female parents and their offspring. The only study to test for coadaptation between male parents and their offspring found no correlation between male care and offspring begging, despite a positive correlation between female care and offspring solicitation (21). The results of our experiment suggest that this difference in coadaptation will reflect differences in genetic architecture underlying care in the 2 sexes as also suggested by the authors of this study (21).…”

“…This highlights the importance of estimates of genetic correlations between parental behaviors within a sex and between the same behaviors in males and females, a crucial piece of information that is lacking in the few other studies examining genetic variation underlying parental care (13,14,19,(21)(22)(23)(24)(25)(26). Such information is essential to our understanding of the evolution of parental care, given that care involves suites of behaviors, and thus the total response to selection depends not only on the genetic variation in the traits of interest but also on their genetic covariation within and between the sexes (10)(11)(12)27).…”

“…The only study to test for coadaptation between male parents and their offspring found no correlation between male care and offspring begging, despite a positive correlation between female care and offspring solicitation (21). The results of our experiment suggest that this difference in coadaptation will reflect differences in genetic architecture underlying care in the 2 sexes as also suggested by the authors of this study (21). This hypothesis for differences in parent-offspring coadaptation within a species could be tested in burying beetles, as we now predict that there will be no genetic correlation between male provisioning (direct care) and offspring solicitation because of the difference in the genetic architecture influencing direct care in male and female burying beetles.…”