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In many nuclear families, dependent offspring receive unequal shares of parental investment. Initial overproduction can be adaptive from the perspective of parents, but parents must be able to identify appropriate candidates for favourite status. We studied early nestling development in house sparrows (Passer domesticus), a species in which the loss of some brood members is common, testing the prediction that body mass and carotenoid-rich flange colours are important to nestling success. There was substantial variation in both traits within broods, even only 1 day after hatching. Nestlings low in the within-brood mass hierarchy gained more mass if they displayed more carotenoid-rich flanges than broodmates. Position in the colour hierarchy did not, however, predict mass gain for individuals that were heavier than their broodmates. Nestlings that were heavier or had more carotenoid-rich mouths were also less likely to be the victim of brood reduction. Our results suggest that house sparrow parents use both nestling body size and mouth colour when making allocation decisions. Understanding both how and when offspring traits and parental preferences function is key to understanding how selective pressures act on offspring–parent communication. [ABSTRACT FROM AUTHOR]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2009.07.009 Byline: Matthew B. Dugas Abstract: When the potential contributions that offspring can make to parental fitness vary, parents benefit by diverting resources towards the offspring offering the highest return on investment. In birds, nestling begging has been hypothesized to allow parental assessment of the relative contribution that each offspring can make to parental fitness. Although begging is often interpreted as a signal of need, studies of nestling morphology, specifically carotenoid-based mouth colours, suggest that these traits signal not the need, but the quality of the nestlings. Here, I manipulated flange colour in a free-living population of house sparrows with experimental paints that did not feature a UV reflectance peak, but otherwise approximated carotenoid-based colours within the range of natural variation. I presented parents with one nestling that appeared to have the carotenoid-rich rictal flanges associated with high condition and one that appeared to have the carotenoid-poor flange colour associated with poor condition. Parents delivered more food items to the nestling that appeared to have carotenoid-rich flanges, a pattern driven by a strong female bias and a similar, but nonsignificant, trend in males. This study shows that parents attend to these visual signals rather than correlated features of nestling physiology associated with carotenoids. Broadly, this result suggests that at least some components of begging are used by parents to bias resource allocation towards their most promising, rather than most needy, offspring. Author Affiliation: Department of Zoology, University of Oklahoma, U.S.A Article History: Received 13 March 2009; Revised 26 May 2009; Accepted 20 July 2009 Article Note: (miscellaneous) MS. number: A09-00167R

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2009.05.032 Byline: Douglas W. Mock, P.L. Schwagmeyer, Matthew B. Dugas Abstract: Because parental investment for multiple offspring often proves insufficient, diverse taxa have evolved systems for reducing family size secondarily. We found brood reduction to be common (42% of 1000 nesting cycles) in Oklahoma house sparrows, Passer domesticus, especially when families of four or more nestlings were furnished with less food. Whereas deliveries of large-bodied prey have been shown previously to predict long-term survival of nestlings (to breeding age), smaller prey items appear adequate for short-term survival (to fledging). Parents did not prune deliveries in the aftermath of brood reduction, thereby bestowing a likely food bonus on surviving siblings. Individual male and female parents that were observed for multiple nesting cycles produced similar measures of day 11 offspring mass (including largest chick, smallest chick, and brood mean). By contrast, an index of overall sibling mass inequality was not repeatable. Parents skewed food deliveries towards the larger members of relatively passive day 3 broods, probably influencing early mortality: median age for brood reduction was day 4 posthatching. Patterns of allocation that can be inferred from mass inequities of older chicks (on day 11) also pointed to persistently skewed deliveries; nestlings underweight at that age were more likely to die without fledging. Large broods early in the season tended to have nestlings less equally sized than broods late in the season, whereas small broods showed no such season effect. Brood reduction appears advantageous to parents if surviving offspring thereby increase prefledging mass sufficiently to compensate for the drop in numbers. Author Affiliation: Department of Zoology, University of Oklahoma, U.S.A. Article History: Received 26 January 2009; Revised 5 March 2009; Accepted 28 May 2009 Article Note: (miscellaneous) MS. number: A09-00058R

Exposure to maternally derived steroids during embryonic development can elicit phenotypic effects in the resulting offspring. Studies of maternal steroid effects, especially rich in mammals and birds, have offered exciting insights into the evolution of maternal effects in vertebrates. To extend this literature, we quantified levels of steroids in the eggs of four neotropical dendrobatid frogs that lay terrestrial clutches, a reproductive strategy that has evolved multiple times in amphibians. Building on our observational results, we then manipulated levels of pregnenolone and progesterone in eggs of one species and examined how this affected steroid levels during development. Eggs of all four species had detectable steroids levels, with progestogens being more abundant than androgens and glucocorticoids. Estrogens could not be detected. Immersion of frog eggs in a solution containing pregnenolone and progesterone resulted in elevated levels of both steroids early in development, but levels declined and were similar to those in unmanipulated eggs by the end of development. Treated eggs also exhibited a transient increase in levels of steroids that can be produced from pregnenolone and progesterone. Overall, our findings demonstrate that frog eggs contain steroids similar to what has been observed in other egg‐laying vertebrates. During development, steroid levels are dynamic, further suggesting developing embryos regulate exposure to maternal steroids. These results set the stage for investigating the causes and consequences of maternal steroid effects in frogs. Highlights: Frog eggs contain a wide variety of steroids at the time they are laidSteroid levels within eggs can be manipulated by immersing eggs in water that contains steroidsDuring embryonic development, steroid levels within eggs decline [ABSTRACT FROM AUTHOR]

Parasites have profound and widespread implications for the ecology and evolution of hosts, and human activity has increased the frequency of interactions between hosts and parasites that have not co-evolved. For example, by building habitat attractive for nesting, humans might have facilitated range expansion by cliff swallows (Petrochelidon pyrrhonata) and barn swallows (Hirundo rustica) in North America, concurrently allowing a haematophagous ectoparasite of cliff swallows, the swallow bug (Oeciacus vicarious), to infest the nests of barn swallows. We found that in barn swallow nests infested with swallow bugs, nestlings weighed less and had lower haematocrit, and the within-brood variation in body mass and tarsus length was higher. Information about these negative effects might be available to parents via mouth coloration, a condition-dependent component of the begging signal. We found that nestlings from infested broods had lower-intensity carotenoid-based and ultraviolet mouth colours, although most elements of colour were unrelated to parasites. Host switching by the swallow bug offers excellent opportunities to understand the direct and indirect effects of a novel parasite and might also afford insights into how parasites cope with selective pressures exerted by closely related hosts with key ecological differences. [ABSTRACT FROM AUTHOR]

Anti-predator strategies can influence trade-offs governing other activities important to fitness. Crypsis, for example, might make conspicuous sexual display especially costly, whereas aposematism might reduce or remove such costs. We tested for correlates of anti-predator strategy in Oophaga pumilio , a polytypic poison frog with morphs spanning the crypsis–aposematism continuum. In the wild, males of visually conspicuous morphs display from conspicuous perches and behave as if they perceive predation risk to be low. We thus predicted that, given a choice of ambient light microhabitats, these males would use high ambient light conditions the most and be most likely to perch in high-light conditions. We found no evidence that differently colored male O. pumilio preferentially used bright microhabitats or that ambient light influenced perching in a morph-specific manner. Independent of light conditions, males from the most conspicuous population perched the least, but the most conspicuous individuals from a polymorphic population perched the most. These patterns suggest that preferences do not necessarily underlie among-morph differences observed in the wild. This could be explained, and remain consistent with theory, if risk aversion is shaped, in part, by experience. [ABSTRACT FROM AUTHOR]

The mouth coloration of nestling birds is hypothesized to be uniquely adaptive during the nestling stage, perhaps signalling condition. To identify nestling-specific colours, we compared adult and nestling gapes in Cave Swallows (Petrochelidon fulva). Nestling gapes reflected more ultraviolet (UV) light and tended to be yellower (because they contained carotenoids). Across broods, heavier nestlings had yellower, less bright, and less UV-rich flanges, and less bright gapes. Nestlings with carotenoid-rich plasma had brighter flanges and yellower gapes. Color did not, however, signal within-brood status. Studies of nestling mouth coloration may benefit from considering complementary and/or competing roles of the trait across ontogeny. [ABSTRACT FROM AUTHOR]

Care that parents provide to offspring often comes at the cost of other reproductive opportunities, generating parent-offspring conflict and sibling rivalry whenever there are resource shortfalls. Although these family dynamics are most often studied in birds, convergent family structures can be found in diverse lineages, including in frogs that feed their developing young with unfertilized trophic eggs. We used observations in a captive colony of the strawberry poison frog (Oophaga pumilio) to test the hypothesis that parental care is a limiting resource within families of this egg-feeding frog, and thus could generate conflicts of interest. We found that maternal provisioning was valuable to offspring: Trophic egg provisioning was positively associated with larval survival, size at metamorphosis, and postmetamorphic survival. Maternal care came at the cost of other reproductive opportunities: Females produced fewer reproductive clutches when caring for tadpoles than when dependent young were absent. Even under presumably benign captive conditions, resources were limited within reproductive cycles. Tadpoles in larger broods received smaller meals, and although survival increased across brood sizes of 1-3 tadpoles, the largest broods (4 tadpoles) suffered reduced survival. Finally, older tadpoles received larger meals, a pattern consistent with the prediction that females would favor their most valuable offspring. These results suggest that relationships within O. pumilio families are constrained by resource limitation. Because of a convergent family structure coupled with substantial metabolic and natural history differences, egg-feeding frogs will provide an excellent complement to birds when addressing the causes and consequences of conflicts of interest within families. [ABSTRACT FROM AUTHOR]