| DatasetID | 254 |
|---|---|
| Name | Acorn Woodpecker DNA fingerprints |
| Description | "Reproductive skew in the polygynandrous acorn woodpecker." Abstract: Reproductive skew models, which focus on the degree to which reproduction is shared equally (low skew) or monopolized by a single individual (high skew) within groups, have been heralded as providing a general unifying framework for understanding the factors determining social evolution. Here, we test the ability of optimal skew, or ‘‘transactional,’’ models, which predict the level of skew necessary to promote stable associations of dominants and subordinates, rather than independent breeding, to predict reproductive partitioning in the acorn woodpecker (Melanerpes formicivorus). This species provides a key test case because only a few vertebrates exhibit polygynandry (multiple breeders of both sexes within a group). Contrary to the predictions of the models, joint-nesting females share reproduction more equitably than expected, apparently because egg destruction and the inability of females to defend their eggs from cobreeders eliminate any possibility for one female to control reproduction. For males, however, reproductive skew is high, with the most successful male siring over three times as many young as the next most successful male. Although this result is consistent with optimal skew models, other aspects of male behavior are not; in particular, the repro- ductively most successful male frequently switches between nests produced by the same set of cobreeders, and we were unable to detect any phenotypic correlate of success. These results are consistent with an alternative null model in which cobreeder males have equal chance of paternity, but paternity of offspring within broods is nonindependent as a consequence of female, rather than male, control. We estimated these parameters from 28 years of continuous study (1972 to 1999) on a marked population at Hastings Reservation in Monterey County, CA (19–27), during which time we followed the life-histories of over 3,000 color-banded individuals (Table 1). "Shared parentage and incest avoidance in the cooperatively breeding acorn woodpecker." Abstract: Social groups of acorn woodpeckers (Melanerpes formicivorus) range in size from unaided pairs to 15 adults. Behavioural indicators of mate guarding, assumed incest avoidance and observations of egg-laying indicate that social organization ranges from monogamous pairs to groups with up to seven male and three female putative cobreeders plus up to 10 nonbreeding helpers. In addition, groups occasionally lack a putative breeder throughout the breeding season. Here we report results from multilocus DNA fingerprinting of 372 nestlings from 123 nests in groups with putative cobreeders of one or both sexes. No extra-group fertilizations were found. Putative cobreeding males within social groups shared paternity. However, the most reproductively successful male was, on average, almost three times as successful as the next most successful and additional males only occasionally sired offspring. In contrast, cobreeding females shared parentage equally. Helpers never bred incestuously when their opposite-sex parent (or another relative, such as their uncle) held breeding status in the group. However, during breeding male vacancies, 14 nestlings were produced when helper males bred incestuously with their mother. Both male and female helpers usually became successful cobreeders with their same-sex parent following replacement of the opposite-sex breeder(s) by unrelated individuals. Nestling sex ratio variation in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus). Abstract: We examined sex ratio variation in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus) over a 27-year period in central coastal California. The sex ratio of eggs is even or possibly biased toward females. However, hatching asynchrony and brood reduction differentially favor the slightly larger males such that the sex ratio when young become self-sufficient is 54.0% males, slightly but significantly different from 50:50. This bias, or at least the differential mortality that produces it, does not appear to be explainable by any of the major hypotheses for an overall sex bias. These include the repayment model, local resource competition, and sexual size dimorphism, all of which predict a female bias or a male bias significantly smaller than that observed. On an individual level, we found no evidence for facultative sex ratio manipulation related to annual differences in the acorn crop, apparent seasonal declines in food availability, or differences in territory quality. We also found no evidence for a non-binomial distribution of sexes within broods despite the potential fitness benefits of creating large coalitions of same-sexed siblings. Males inherit their natal territories more frequently than do females, and we speculate that birds may invest more in sons either to increase the probability that they will be able to pass along their territory to their descendants or to facilitate their sons' ability to compete as future cobreeders. Alternatively, acorn woodpeckers may be unable to fully compensate for the ancillary bias caused by differential juvenile survivorship, leading to unequal investment in the sexes contrary to the prediction of Fisher. Opposite to what has been found in other birds and mammals, the faster growth and larger size of male nestlings appears to confer a survival benefit rather than a cost. |
| Physical Location | |
| Publisher/Owner | Joe Haydock, Gonzaga University, 509-323-6704 |
| Publication Date | |
| Permissions | Undetermined |
| Source | Mark Stromberg NRS file |
| Contact | Joe Haydock |
| Type | Biological Survey - Observational |
| Subject | Animal |
| Geo. Extent | Hastings Reserve |
| URL | https://berkeley.app.box.com/files/0/f/372728021/1/f_3020747863 |
| NRS Registry? | yes |
| Format | Database |
| Timespan Start | 1974 |
| Timespan End | |
| Total Items | |
| Databased Items | (as of 2012-08-28) |
| Comments | Links are: Haydock, J. and D. Koenig Walter (2002). "Reproductive skew in the polygynandrous acorn woodpecker." Proceedings of the National Academy of Sciences of the United States of America 99(10): 7178-7183. https://berkeley.app.box.com/files/0/f/372728021/1/f_3020747863 Haydock, J., W. D. Koenig, et al. (2001). "Shared parentage and incest avoidance in the cooperatively breeding acorn woodpecker." Molecular Ecology 10(6): 1515-1525. https://berkeley.app.box.com/files/0/s/incest/1/f_3020750105 Koenig Walter, D. and J. Haydock (2001). "Dividing up the kids." Science (Washington D C) 291(5503): 442-443. Can be found online at http://www.sciencemag.org/content/291/5503/442.full Koenig Walter, D., T. Stanback Mark, et al. (2001). "Nestling sex ratio variation in the cooperatively breeding acorn woodpecker (Melanerpes formicivorus)." Behavioral Ecology & Sociobiology49(5): 357-365. https://berkeley.app.box.com/files/0/f/372728021/1/f_3029711773 |
| Entered By | Jessica Rothery |
| Last Updated | 2015-12-27 14:46:09 |