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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]

Young animals often solicit care from their parents using behaviors and morphologies collectively termed begging. Many nestling altricial birds add to their familiar postures and vocalizations by displaying colorful mouthparts, hypothesized to enhance their visual conspicuousness and/or be favored by choosy parents. We evaluated these two hypotheses with experimental manipulations of the flange tissue of house sparrow (Passer domesticus) nestlings. We allowed parents to interact with nestlings that appeared to have either carotenoid-rich or carotenoid-poor flanges, and then with nestlings that appeared similar in carotenoid-richness but differed in either brightness (total light reflected) or ultraviolet (UV) richness. These three features of flange color comprise much of the variation observed both within and among species. None of our three manipulations shaped parents' ability to transfer prey efficiently to nestlings, a proxy for how visually detectable nestlings were. Parents preferentially allocated prey to nestlings that appeared carotenoid-rich, but did not bias allocation when we manipulated brightness or UV reflectance. These patterns suggest that nestlings displaying carotenoid-rich flanges benefit from parental favoritism, but that variation in brightness and UV reflectance do not independently shape parental care, at least within the range a house sparrow parent might encounter in nature. Efforts to understand mouth color in the context of offspring-parent communication and visual signal evolution may benefit from considering the component parts of color, as they may function, be constrained, and evolve independently. [ABSTRACT FROM AUTHOR]

Feeding offspring is a form of care common in animals. How food shapes offspring fitness, and thus selection on parents, is limited by plasticity in offspring growth and development, and such limitation may shape the evolution of parental care. We compared plastic responses to egg feeding, food availability in the nursery, and nursery size in larvae of two poison frogs: Ranitomeya imitator, regularly fed trophic eggs by their mothers in the wild, and R. variabilis tadpoles, which only rarely have the opportunity to consume eggs. Hand‐reared R. imitator, but not R. variabilis, were heavier at metamorphosis when offered eggs. Although R. imitator ate more of the eggs we offered, perhaps explaining this proximately, the greater plasticity of R. imitator persisted when we manipulated the quantity of an egg‐free diet meant to approximate food in a natural nursery. Egg feeding did not influence the length of the larval period, and only tadpole R. variabilis took longer to complete metamorphosis in more food‐rich nurseries, as is predicted for amphibians generally. In large nurseries, individuals of both species spent longer as tadpoles and were heavier at metamorphosis, an effect independent of food, and one that reflects the complex relationship between ecology and amphibian development. These species differences highlight how tadpole traits might constrain the evolution of egg feeding: R. imitator feed eggs to their tadpoles, and their tadpoles, unlike R. variabilis (a presumptive proxy for the non‐feeding ancestor), offer high returns on such investment. Comparative work will offer the exciting opportunity to assess the extent to which egg feeding selected for this growth response to food availability and/or this plasticity facilitated the evolution of care. [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]

Codivergence of mating traits and mate preferences can lead to behavioral isolation among lineages in early stages of speciation. However, mate preferences limit gene flow only when expressed as mate choice, and numerous factors might be more important than preferences in nature. In the extremely color polytypic strawberry poison frog (Oophaga pumilio), female mate preferences have codiverged with color in most allopatric populations tested. Whether these lab-assayed preferences predict mating (gene flow) in the wild remains unclear. We observed courting pairs in a natural contact zone between red and blue lineages until oviposition or courtship termination. We found color-assortative mating in a disturbed habitat with high population density but not in a secondary forest with lower density. Our results suggest color-assortative O. pumilio mate choice in the wild but also mating patterns that do not match those predicted by lab-assayed preferences. [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]

The discovery of a trait in a new lineage, especially one distantly related to those already known to express the trait, affords the opportunity to test and refine existing hypotheses for that trait’s evolution and to develop new ideas. Peter Weygoldt made such a discovery, reporting the first instance of a frog that feeds its young and, even more remarkably, the first instance of dependent tadpoles that perform solicitation displays before being fed ( 1980. Behav. Ecol. Sociobiol. 7, 329–332 ). This discovery has featured prominently in taxonomic surveys of parental care and offspring-parent communication, but more importantly has expanded the questions that are and can be asked about these topics. I review the advances in knowledge of the natural history of the frog Weygoldt studied as well as the theoretical frameworks that inform and are informed by these advances. I highlight ideas and information about parental care in O. pumilio that are central to broadly understanding the evolution of parental care. Our understanding of the evolution of sex roles will, for example, improve by following Weygoldt’s finding that male O. pumilio care for clutches with detailed accounting of the costs and benefits mothers and fathers might pay for performing this task. When a parent transports tadpoles from a terrestrial clutch to an aquatic nursery, it sets the stage for sibling competition for this resource (transport), and proximate and ultimate tests for such conflict will inform more general ideas about how conflict and cooperation shape nuclear families. That the begging displays of tadpole O. pumilio are performed in solitary nurseries makes this species uniquely suited to test honest-signaling models for the evolution of offspring-parent communication. By detailing the implications and possibilities stemming from Weygoldt’s work, I hope to inspire readers to follow Weygoldt’s lead and his example of careful and detailed observation. [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]

Reproductive isolation is central to the generation of biodiversity, yet a clear understanding of the contributions of alternative reproductive barriers to this process remains elusive. Studies of young lineages that have diverged in ecologically important traits can offer insights into the chronology and relative importance of various isolating mechanisms during speciation. In poison frogs ( Dendrobatidae), within-species lineages often differ dramatically in coloration, a trait subject to natural and sexual selection. Coloration in the strawberry poison frog ( Oophaga pumilio) is particularly diverse and previous work suggests the potential for reproductive isolation. We used a captive breeding experiment to assess the extent of reproductive isolation among three allopatric, genetically distinct O. pumilio lineages that differ in coloration. We compared reproduction of within- and between-lineage pairs, predicting that if lineages are isolated, within-lineage pairs would be most successful. We also examined the fertility and productivity of F1 backcrosses of admixed offspring. We found no evidence suggesting behavioural pre-zygotic or post-zygotic reproductive isolation, indicating that isolation would not be maintained by intrinsic mechanisms in the event of secondary contact. Future work should address costs of between-lineage matings exerted by extrinsic natural and/or sexual selection against admixed offspring. [ABSTRACT FROM AUTHOR]

The phenomenon of aposematism, or the pairing of antipredator defence with conspicuous or distinctive signals, serves as an excellent example of how traits act in concert to shape fitness. Not only does this complex phenotype require the integration of multiple traits, it alters the fitness pay-offs of yet others. The protection offered by aposematism may, for example, reduce the costs associated with foraging or sexual display. Thus, well-protected aposematic lineages should be bolder, more active and less likely to respond to perceived threats of predation than more cryptic lineages. Comparisons of differently coloured morphs of the polytypic strawberry poison frog ( Oophaga pumilio) have supported the predicted behavioural correlates of aposematism, with the exception of those regarding responsiveness to simulated predators. We tested the key prediction that aposematic coloration will be associated with reduced sensitivity to predators in two polymorphic O. pumilio populations. The novel approach of studying polymorphic populations allowed us to assess the effect of colour in the absence of potentially confounding habitat differences. We found that colour was associated with the probability that a frog would attempt escape and the distance at which it fled, but only in one population, and not in the predicted direction. An overall comparison of the two populations superficially supported our predictions, but this pattern actually arose because frogs occupying higher perches were less likely to respond, a pattern that may reflect the value of high perches and the costs associated with returning to them after attempted escape. These results highlight the complexity of the relationship between predators and prey, the challenges associated with understanding how and why traits are correlated, and the intimate ties between behaviour and morphological evolution. [ABSTRACT FROM AUTHOR]

The assumption that reproduction is costly is central to life-history theory. Good evidence supporting this premise comes from studies, mostly in short-lived invertebrates, demonstrating a negative relationship between reproduction and longevity. Whether this trade-off operates broadly, for example in males and females and in short- and long-lived organisms, remains unresolved. We found a negative relationship between reproduction and days survived in captive, wild-caught, individuals of a long-lived poison frog with biparental care ( Oophaga pumilio). The proportion of time that individuals spent paired and tadpole production rate were negatively associated with days survived in both sexes, and clutch production was negatively associated with days survived in females. These results broaden the taxonomic base upon which this tenet of life-history theory is built, empirically confirm that females of this species should be choosy when selecting mates and caring for offspring, and suggest that the costs of 'limited' male care in this species deserve re-evaluation. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115, 211-218. [ABSTRACT FROM AUTHOR]

Dependent offspring influence allocation of parental investment using specialized traits thought to contain information about offspring condition. To test this hypothesis, we examined the relationship between one component of avian begging, the phenotype of the nestling mouth, and the density of a haematophagous mite, Pellonyssus reedi, in nestling House Sparrows Passer domesticus. Ectoparasite density in broods was negatively associated with average nestling mass and flange colour intensity and positively associated with mouth width, but was not related to the intensity of blood-based gape coloration or flange width. These results support the hypothesis that components of offspring solicitations signal high quality, and highlight the diverse selective pressures shaping offspring–parent communication. [ABSTRACT FROM AUTHOR]

Amphibians are currently experiencing the most severe declines in biodiversity of any vertebrate, and their requirements for successful reproduction are poorly understood. Here, we show that supplementing the diet of prey items (fruit flies) with carotenoids has strong positive effects on the reproduction of captive strawberry poison frogs ( Oophaga pumilio), substantially increasing the number of metamorphs produced by pairs. This improved reproduction most likely arose via increases in the quality of both the fertilized eggs from which tadpoles develop and trophic eggs that are fed to tadpoles by mothers. Frogs in this colony had previously been diagnosed with a Vitamin A deficiency, and this supplementation may have resolved this issue. These results support growing evidence of the importance of carotenoids in vertebrate reproduction and highlight the nuanced ways in which nutrition constrains captive populations. Zoo Biol. 32:655-658, 2013. © 2013 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Dependent offspring use specialized traits to attract parental care. In birds, this includes morphological ornaments (e.g. colourful plumage or mouthparts) that are associated with nestling condition and shape the allocation of parental care. Ornament expression often differs among broods, even after differences in individual condition are accounted for statistically. Understanding how this variation arises is important for understanding the information content of these signals, their functional importance, and their evolution. The present study used a cross-fostering experiment to assess the relative contributions of parental effects to among-brood differences in the mouth coloration of nestling house sparrows, specifically the carotenoid-richness, overall brightness, and ultraviolet (UV) coloration of rictal flanges. The expression of carotenoid-based coloration was explained by synchronous breeding, nest-of-rearing and nest-of-origin. Brightness and relative UV intensity, however, were explained only by synchronous breeding, and there was substantial unexplained variation in all three colour parameters. Among-brood variation in mouth coloration, then, may primarily contain information about the environment in which offspring are reared. At the individual level, ontogenetic changes in the carotenoid-richness and brightness of flanges positively reflected mass gain (a proxy for food intake). Larger and yellower chicks gained more mass, consistent with parental preferences for these traits. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106, 169-179. [ABSTRACT FROM AUTHOR]

An often underappreciated function of signals is to notify receivers of the presence and position of senders. The colours that ornament the mouthparts of nestling birds, for example, have been hypothesized to evolve via selective pressure generated by parents' inability to efficiently detect and feed nestlings without such visually conspicuous targets. This proposed mechanism has primarily been evaluated with comparative studies and experimental tests for parental allocation bias, leaving untested the central assumption of this detectability hypothesis, that provisioning offspring is a visually challenging task for avian parents and conspicuous mouths help. To test this assumption, I manipulated the mouths of nestling house sparrows to appear minimally and maximally conspicuous, and quantified prey transfer difficulty as the total duration of a feeding event and the number of transfer attempts required. Prey transfer to inconspicuous nestlings was, as predicted, more difficult. While this suggests that detectability constraints could shape nestling mouth colour evolution, even minimally conspicuous nestlings were not prohibitively difficult for parents to feed, indicating that a more nuanced explanation for interspecific diversity in this trait is needed., (© 2015 The Author(s).)