Biomedical subjects

Ben C Sheldon

Publications and source records attributed to Ben C Sheldon.

22 records · Page 2Linked to original sources

PubMed2002

Severe inbreeding depression in collared flycatchers (Ficedula albicollis).

The causes and magnitude of inbreeding depression are of considerable importance for a wide range of issues in evolutionary and conservation biology, but we have only a limited understanding of inbreeding depression in natural populations. Here, we present a study of inbreeding in a large wild population of collared flycatchers (Ficedula albicollis). Inbreeding was rare, to the extent that we detected only 1.04% of 2139 matings over 18 years that resulted in offspring with a non-zero inbreeding coefficient, f > 0. When it did occur, inbreeding caused a significant reduction in the egg-hatching rate, in fledgling skeletal size and in post-fledging juvenile survival, with the number of offspring being recruited to the breeding population from a nest of f = 0.25 being reduced by 94% relative to a non-inbred nest. A maximum-likelihood estimate of the number of lethal equivalents per gamete was very high at B = 7.47, indicating a substantial genetic load in this population. There was also a non-significant tendency for inbreeding depression to increase with the strength of selection on a trait. The probability of mating between close relatives (f = 0.25) increased throughout the breeding season, possibly reflecting increased costs of inbreeding avoidance. Our results illustrate how severe inbreeding depression and considerable genetic load may exist in natural populations, but detecting them may require extensive long-term datasets.

Animals↗

PubMed2002

Experimental analysis of sperm competition mechanisms in a wild bird population.

Recent work on wild birds has revealed the importance of sperm competition as a source of sexual selection, but behavioral and paternity studies have previously provided only indirect evidence for mechanisms of sperm competition in wild birds. In a field study of collared flycatchers Ficedula albicollis we used a previously uncharacterized method to determine the frequency and timing of extra-pair inseminations. By counting the number of sperm trapped on the perivitelline layer of eggs, we determined the timing of inseminations and estimated, on a day-to-day basis, the amount of sperm females stored. Our results showed that female collared flycatchers preferentially engaged in extra-pair copulations when mated to an unattractive male with a small white forehead patch. These copulations were timed for the middle part of their fertile period, at least 2 days after the last within-pair insemination. Although the mean number of extra-pair insemination events was only 1.33 per cuckolding female, the ratio between the number of sperm from extra-pair and pair inseminations was at least 5 to 1. Thus a single, well timed extra-pair insemination caused by female behavior could greatly bias fertilization probability in favor of an attractive extra-pair male. Our results suggest a possible behavioral mechanism for female control of sperm competition.

Animals↗

PubMed2002

Relating paternity to paternal care.

Intuition suggests, to most people, that parents should be selected to care for their offspring in relation to how certain they are of being the parents of those offspring. Theoretical models of the relationship between parental investment and certainty of parentage predict the two to be related only when some other assumptions are made, few of which can be taken for granted. I briefly review the models and their assumptions, and discuss two kinds of difficulty facing an empiricist wishing to test the models. The first is the problem of unmeasured (and immeasurable) variables. The second is the problem that even the most extensive models do not capture the complexity that can be demonstrated in real systems. I illustrate some of these problems, and some qualitative tests of the models, with experimental work on a population of the collared flycatcher. My conclusion is that although there are some cases where the models have qualitative support, we are a long way from understanding whether paternal care is commonly adjusted in relation to certainty of paternity.

Animals↗

PubMed2002

Constraints in the evolution of sex ratio adjustment.

When the relative fitness of male and female offspring varies with environmental conditions, evolutionary theory predicts that parents should adjust the sex of their offspring accordingly. Qualitative and even quantitative support for this prediction is striking in some taxa but much less convincing in others. Explaining such variation across taxa in the fit of sex ratio theory remains a major challenge. We use meta-analysis to test the role of two constraints in the evolution of sex ratios. Based on analysis of sex ratio skews in birds and wasps, we show that (i) mechanisms of sex determination do not necessarily constrain the evolution of sex ratio adjustment, and (ii) parental ability to predict their offsprings' environment influences the evolution of sex ratio patterns across taxa. More generally, our results show that multiple constraints may determine the precision of adaptation.

Adaptation, Physiological↗