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Butler JM, McKinney JE, Ludington SC, Mabogunje M, Baker P, Singh D, Edwards SV, O'Connell LA. Tadpoles rely on mechanosensory stimuli for communication when visual capabilities are poor. Dev Biol 2024; 514:66-77. [PMID: 38851558 DOI: 10.1016/j.ydbio.2024.05.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2023] [Revised: 05/08/2024] [Accepted: 05/10/2024] [Indexed: 06/10/2024]
Abstract
The ways in which animals sense the world changes throughout development. For example, young of many species have limited visual capabilities, but still make social decisions, likely based on information gathered through other sensory modalities. Poison frog tadpoles display complex social behaviors that have been suggested to rely on vision despite a century of research indicating tadpoles have poorly-developed visual systems relative to adults. Alternatively, other sensory modalities, such as the lateral line system, are functional at hatching in frogs and may guide social decisions while other sensory systems mature. Here, we examined development of the mechanosensory lateral line and visual systems in tadpoles of the mimic poison frog (Ranitomeya imitator) that use vibrational begging displays to stimulate egg feeding from their mothers. We found that tadpoles hatch with a fully developed lateral line system. While begging behavior increases with development, ablating the lateral line system inhibited begging in pre-metamorphic tadpoles, but not in metamorphic tadpoles. We also found that the increase in begging and decrease in reliance on the lateral line co-occurs with increased retinal neural activity and gene expression associated with eye development. Using the neural tracer neurobiotin, we found that axonal innervations from the eye to the brain proliferate during metamorphosis, with few retinotectal connections in recently-hatched tadpoles. We then tested visual function in a phototaxis assay and found tadpoles prefer darker environments. The strength of this preference increased with developmental stage, but eyes were not required for this behavior, possibly indicating a role for the pineal gland. Together, these data suggest that tadpoles rely on different sensory modalities for social interactions across development and that the development of sensory systems in socially complex poison frog tadpoles is similar to that of other frog species.
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Affiliation(s)
- Julie M Butler
- Department of Biology, Stanford University, United States.
| | | | | | - Moremi Mabogunje
- Department of Biology, Stanford University, United States; Foothill Community College, United States
| | - Penelope Baker
- Department of Biology, Stanford University, United States
| | - Devraj Singh
- Department of Organismic and Evolutionary Biology, Harvard University, United States; Museum of Comparative Zoology, Harvard University, United States; Department of Biology, University of Kentucky, United States
| | - Scott V Edwards
- Department of Organismic and Evolutionary Biology, Harvard University, United States; Museum of Comparative Zoology, Harvard University, United States
| | - Lauren A O'Connell
- Department of Biology, Stanford University, United States; Wu Tsai Institute for Neuroscience, Stanford University, United States.
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2
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Duncan PA, Tauber AM, Sakaluk SK, Thompson CF. INTERACTIVE EFFECTS OF INCREASED NESTBOX TEMPERATURE AND VITAMIN E ON NESTLING GROWTH ARE ATTENUATED BY PLASTICITY IN FEMALE INCUBATION EFFORT. Ethology 2024; 130:e13421. [PMID: 38389708 PMCID: PMC10881224 DOI: 10.1111/eth.13421] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Accepted: 10/19/2023] [Indexed: 02/24/2024]
Abstract
In recent years, temperatures have increased globally, and nestlings of many bird species are likely regularly exposed to increased temperatures both pre- and postnatally. Even small increases in nest temperature during incubation affect offspring growth and survival in a variety of species, one cause of which is thought to be increased production of prooxidants in embryos and nestlings. Defences marshalled in response to this oxidative stress could, in turn, result in trade-offs that lead to reduced survival or growth. If so, any downstream negative effects on nestlings of increased ambient temperatures during incubation could be counteracted by increasing their antioxidant intake. We predicted, therefore, that dietary supplements of an antioxidant would reduce or eliminate any detrimental effects on nestling growth and survival of experimentally increased nest temperature during the incubation period. We employed a split-brood design in which we increased nest temperature of entire clutches and, after hatching, provided dietary supplements of the antioxidant vitamin E to half of the nestlings within broods. We also recorded female incubation and provisioning behaviour to control for the possibility that heating nests might also influence maternal behaviour. There was a significant interaction between nestbox heating treatment and vitamin E treatment in their effect on nestling mass, a trait that is positively correlated with survival and future reproductive success in the study population. Vitamin E supplementation promoted increased nestling mass in heated nests, whereas it had the opposite effect in control nests, but these effects were weak. Heating significantly affected female incubation behaviour, with females in heated nestboxes investing less in incubation than those in unheated boxes. These results suggest that within at least some range of expected increased ambient temperatures during the 21st century, effects of climate change on nestling bird development can be mitigated by adjustments in female incubation behaviour.
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Affiliation(s)
- Paige A. Duncan
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University
| | - Ashley M. Tauber
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University
| | - Scott K. Sakaluk
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University
| | - Charles F. Thompson
- Behavior, Ecology, Evolution, and Conservation Section, School of Biological Sciences, Illinois State University
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3
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Wang D, Zhang W, Yang S, Richter XYL. Sex differences in avian parental care patterns vary across the breeding cycle. Nat Commun 2023; 14:6980. [PMID: 37914691 PMCID: PMC10620184 DOI: 10.1038/s41467-023-42767-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2022] [Accepted: 10/20/2023] [Indexed: 11/03/2023] Open
Abstract
Parental care in birds consists of elaborate forms across stages, including nest building, incubation, and offspring provision. Despite their evolutionary importance, knowledge gaps exist in the extent to which parents contribute disproportionately to these forms and factors that are associated with variations in care patterns between sexes. Here, we analyzed 1533 bird species and discovered remarkable variability in care patterns. We show that parental care should not be viewed as a unitary trait but rather as a set of integrated features that exhibit considerable temporal and sex-specific variation. Our analyses also reveal moderate consistency in care patterns between breeding stages, pointing towards shared intrinsic factors driving sex-specific care. Notably, we found that species experiencing strong sexual selection on males or species facing paternity uncertainty display a tendency towards female-biased care. This work advances our understanding of the temporal variations in sex-specific contributions to avian parental care and their potential evolutionary drivers.
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Affiliation(s)
- Daiping Wang
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang, 100101, Beijing, China.
- University of Chinese Academy of Sciences, 100049, Beijing, China.
| | - Wenyuan Zhang
- Edward Grey Institute, Department of Biology, University of Oxford, Oxford, OX1 3SZ, UK
- Department of Biology, Quebec Centre for Biodiversity Science, McGill University, Montreal, QC, H3A 1B1, Canada
| | - Shuai Yang
- Key Laboratory of Animal Ecology and Conservation Biology, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang, 100101, Beijing, China
- University of Chinese Academy of Sciences, 100049, Beijing, China
| | - Xiang-Yi Li Richter
- Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, CH-3012, Bern, Switzerland.
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4
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Zepeda JA, Bautista A, Féron C, Martínez-Gómez M, Robles-Guerrero F, Reyes Meza V, Hudson R, Rödel HG. Patterns and predictors of inter-litter differences in rabbit pup locomotor activity, based on an automatized quantification method. Physiol Behav 2023; 261:114089. [PMID: 36657652 DOI: 10.1016/j.physbeh.2023.114089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2022] [Revised: 01/12/2023] [Accepted: 01/13/2023] [Indexed: 01/18/2023]
Abstract
Individual-level sibling interactions in the litter huddle have been studied extensively, especially in the domestic rabbit (Oryctolagus cuniculus). However, little is known about inter-litter differences in pup activity patterns during early postnatal life, in particular regarding the drivers of such variation. In our study on 2-3-day-old rabbit pups, we predicted lower locomotor activity in litters with lower mean body masses on the day of birth (starting body mass) and with lower daily milk intake per pup, possibly constituting a behavioral strategy of pups to cope with associated energetic constraints. For an automatized assessment of pup locomotor activity in the litter huddle, we successfully developed and validated a method based on the quantification of dissimilarities between consecutive frames of video footage. Using this method, we could confirm a U-shaped time course of litter-level locomotor activity, with maximum values shortly before and after the once-daily nursing typical for the rabbit. As predicted, between-litter variation in mean starting body mass and in daily milk intake affected the degree of locomotor activity in the litter huddle, in an interactive way. That is, in litters with heavier starting body masses, pup locomotor activity was greater in pups with an initially higher milk intake, suggesting that only pups with better body condition and a higher energy intake could afford higher levels of activity. This interaction was exclusively apparent during the middle phase of the 24 h inter-nursing interval, when litter activity was low. Shortly before nursing, when pups show higher levels of locomotor behavior in anticipation of the mother's arrival, and shortly after nursing when the pups were more active possibly due to adjustments of their positions in the huddle, activity levels were decoupled from pups' starting body mass and previous milk intake. Our findings highlight the importance of pup body mass and daily energy intake, two parameters known to be related to maternal characteristics, in shaping inter-litter differences in pup locomotor activity.
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Affiliation(s)
- José Alfredo Zepeda
- Doctorado en Ciencias Biológicas, Universidad Autónoma de Tlaxcala, Mexico; Centro Tlaxcala de Biología de la Conducta, Universidad Autónoma de Tlaxcala, Mexico; Preparatoria Alfonso Calderon Moreno, Benemérita Universidad Autónoma de Puebla, Mexico
| | - Amando Bautista
- Centro Tlaxcala de Biología de la Conducta, Universidad Autónoma de Tlaxcala, Mexico.
| | - Christophe Féron
- Laboratoire d'Ethologie Expérimentale et Comparée UR 4443 (LEEC), Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
| | - Margarita Martínez-Gómez
- Centro Tlaxcala de Biología de la Conducta, Universidad Autónoma de Tlaxcala, Mexico; Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico
| | - Franco Robles-Guerrero
- Laboratoire d'Ethologie Expérimentale et Comparée UR 4443 (LEEC), Université Sorbonne Paris Nord, F-93430 Villetaneuse, France
| | - Verónica Reyes Meza
- Centro Tlaxcala de Biología de la Conducta, Universidad Autónoma de Tlaxcala, Mexico
| | - Robyn Hudson
- Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Mexico
| | - Heiko G Rödel
- Laboratoire d'Ethologie Expérimentale et Comparée UR 4443 (LEEC), Université Sorbonne Paris Nord, F-93430 Villetaneuse, France.
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5
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Fortuna R, D'Amelio PB, Doutrelant C, Ferreira AC, Lecq C, Silva LR, Covas R, Rybak F, Paquet M. Begging and feeding responses vary with relatedness and sex of provisioners in a cooperative breeder. Anim Behav 2022. [DOI: 10.1016/j.anbehav.2021.12.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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6
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Gurguis CI, Duckworth RA. Dynamic changes in begging signal short-term information on hunger and need. Am Nat 2022; 199:705-718. [DOI: 10.1086/719030] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
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7
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Brood sex ratio modulates the effects of extra food on parental effort and sibling competition in a sexually dimorphic raptor. Behav Ecol Sociobiol 2021. [DOI: 10.1007/s00265-021-02970-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
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8
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Parental favoritism in a wild bird population. Anim Cogn 2021; 24:677-687. [PMID: 33398622 DOI: 10.1007/s10071-020-01463-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 12/09/2020] [Accepted: 12/16/2020] [Indexed: 01/14/2023]
Abstract
In most taxa with altricial young, offspring solicit food from their parents using a combination of visual and acoustic stimuli, but exactly what these young are communicating, and how selection shapes parental responses, remains unresolved. Theory posits that parents' interpretation and response to begging should vary with the likelihood of a return on their investment. We tested this in a wild population of prothonotary warblers (Protonotaria citrea), predicting that parents bias food non-randomly toward certain individuals within their broods depending on both the size and number of offspring. We observed parent-offspring interactions and detected strong dependence between brood size and nestling size in shaping parental responses to begging. Larger siblings were less likely to solicit food during feeding events than their smaller siblings, but they received a disproportionate share from parents in nests containing fewer-than-average young, whereas the smaller-than-average nestlings were disproportionately fed in broods containing a greater-than-average number of young. These findings suggest that parents respond to begging signals according to multiple social cues, favoring the stronger siblings with greater survival prospects when few copies of their genes are present, but overtly favoring runts to ensure whole-brood survival when capable of fledging more young. Future experimental studies may shed light on the contributions of parental decision-making and memory, how young nestlings learn in parent-offspring communication systems, and the adaptive significance of these behaviors.
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9
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Jenkins JB, Mueller AJ, Thompson CF, Sakaluk SK, Bowers EK. Female birds monitor the activity of their mates while brooding nest-bound young. Anim Cogn 2021; 24:613-628. [PMID: 33392914 DOI: 10.1007/s10071-020-01453-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 11/19/2020] [Accepted: 11/20/2020] [Indexed: 01/17/2023]
Abstract
In addition to food and protection, altricial young in many species are ectothermic and require that endothermic parents provide warmth to foster growth, yet only one parent-typically the female-broods these young to keep them warm. When this occurs, reduced provisioning by males obliges females to forage instead of providing warmth for offspring, favoring the temporal mapping of male activities. We assessed this in a wild house wren population while experimentally feeding nestlings to control offspring satiety. While brooding, females look out from the nest to inspect their surroundings, and we hypothesized that this helps to determine if their mate is nearby and likely to deliver food to the brood (males pass food to brooding females, which pass the food to nestlings). Females looked out from the nest less often when their partner was singing nearby and when his singing and provisioning were temporally linked, signaling his impending food delivery. Females also left to forage less often when their mate was nearby and likely to deliver food. Nestling begging did not affect these behaviors. Females looking out from the nest more often also provisioned at a higher rate and were more likely to divorce and find a new mate prior to nesting again within seasons, as expected if females switch mates when a male fails to meet expectations. Our results suggest anticipatory effects generated by male behavior and that brooding females temporally map male activity to inform decisions about whether to continue brooding or to leave the nest to forage.
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Affiliation(s)
- Jonathan B Jenkins
- Department of Biological Sciences, Center for Biodiversity Research, Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, 38152, USA.,Department of Biological Sciences, Purdue University, West Lafayette, IN, 47907, USA
| | - Alexander J Mueller
- Department of Biological Sciences, Center for Biodiversity Research, Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, 38152, USA.,National Park Service, Southeast Utah Group, Moab, UT, 84532, USA
| | - Charles F Thompson
- Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, 61790-4120, USA
| | - Scott K Sakaluk
- Behavior, Ecology, Evolution, and Systematics Section, School of Biological Sciences, Illinois State University, Normal, IL, 61790-4120, USA
| | - E Keith Bowers
- Department of Biological Sciences, Center for Biodiversity Research, Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, 38152, USA.
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10
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Bowden-Parry M, Postma E, Boogert NJ. Effects of food type and abundance on begging and sharing in Asian small-clawed otters ( Aonyx cinereus). PeerJ 2020; 8:e10369. [PMID: 33335807 PMCID: PMC7713600 DOI: 10.7717/peerj.10369] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 10/25/2020] [Indexed: 11/23/2022] Open
Abstract
Begging for food, a conspicuous solicitation display, is common in a variety of taxa, and it has received extensive research attention in a parent-offspring context. Both theoretical models and empirical evidence suggest that offspring begging can be an honest signal of hunger or a mediator of competition between siblings. At a behavioural mechanistic level, begging for food can be a form of harassment aimed at persuading those in possession of food to share. Food sharing, defined as the transfer of a defendable food item from one individual to another, can vary considerably between species, age-classes and food type and abundance. We investigated the determinants of begging and food-sharing behaviours in Asian small-clawed otters (Aonyx cinereus), a group-living species that commonly exhibits begging in captivity. We presented two captive otter populations with three food types that varied in exploitation complexity, in three different abundances. We predicted that begging rates would be highest when food was in lowest abundance and hardest to exploit, and that increased begging would lead to increased food sharing. We found that, over time, increased begging rates were indeed correlated with increased food transfers, but neither food type complexity nor abundance affected begging or sharing rates. However, age category was significantly associated with begging and food sharing rates: juvenile otters begged more and shared less than adult otters. The results from this first experimental study on begging and food sharing within the Mustelid family begin to reveal some of the drivers of these behaviours.
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Affiliation(s)
- Madison Bowden-Parry
- Department of Biosciences, University of Exeter, Penryn, Cornwall, United Kingdom
| | - Erik Postma
- Department of Biosciences, University of Exeter, Penryn, Cornwall, United Kingdom
| | - Neeltje J. Boogert
- Department of Biosciences, University of Exeter, Penryn, Cornwall, United Kingdom
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11
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Hodges KE, Mortimer NT, Vrailas-Mortimer AD, Sakaluk SK, Thompson CF. Connecting the dots: avian eggshell pigmentation, female condition and paternal provisioning effort. Biol J Linn Soc Lond 2020; 130:114-127. [PMID: 32394988 DOI: 10.1093/biolinnean/blaa002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2019] [Revised: 01/03/2020] [Accepted: 01/04/2020] [Indexed: 12/13/2022]
Abstract
Differences in avian eggshell pigmentation could be an honest signal of female quality that males use to inform their nestling provisioning effort. We investigated whether among-individual variation in protoporphyrin-based eggshell pigmentation in house wrens (Troglodytes aedon) reflects female fitness-associated traits and whether males use that information. Females laying lighter clutches were older and larger than females laying darker clutches. Nestlings hatching from lighter clutches had greater size-corrected mass on post-hatch day 11, a measure that strongly predicts survival and recruitment to the breeding population. To test whether male provisioning effort responds to clutch pigmentation, we used a reciprocal clutch cross-fostering design, swapping dark with light clutches and light with dark; in controls, we swapped light with light clutches and dark with dark. Shortly before hatching, clutches were returned to their original nest to avoid confounding effects of nestling quality on male provisioning. Contrary to the sexual selection hypothesis, clutch pigmentation had no effect on male provisioning. Males were probably able to observe eggshell pigmentation and thus had information about female quality, but they did not use this information to modulate their nestling provisioning. This may be because of constraints on species-specific reproductive opportunities, or because variation in eggshell protoporphyrin serves other functions.
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Affiliation(s)
- Kara E Hodges
- School of Biological Sciences, Illinois State University,Normal,IL,USA
| | - Nathan T Mortimer
- School of Biological Sciences, Illinois State University,Normal,IL,USA
| | | | - Scott K Sakaluk
- School of Biological Sciences, Illinois State University,Normal,IL,USA
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12
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Mueller AJ, Miller KD, Bowers EK. Nest microclimate during incubation affects posthatching development and parental care in wild birds. Sci Rep 2019; 9:5161. [PMID: 30914752 PMCID: PMC6435697 DOI: 10.1038/s41598-019-41690-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2018] [Accepted: 03/14/2019] [Indexed: 11/08/2022] Open
Abstract
It is widely accepted that recent increases in environmental temperature have had a causal effect on changing life histories; however, much of the evidence for this is derived from long-term observations, whereas inferences of causation require experimentation. Here, we assess effects of increased environmental temperature during incubation on posthatching development, nestling begging and parental care, and reproductive success in two wild, cavity-nesting songbirds, the Carolina wren and prothonotary warbler. We heated experimental nests only during incubation, which increased nest-cavity temperature by ca. 1 °C. This reduced the length of the incubation and nestling periods, and reduced fledging success in prothonotary warblers, while nestling Carolina wrens had similar fledging success but reduced body condition in response to increased temperature. Increased nest-cavity temperature during incubation also reduced posthatching begging by nestlings generally and parental care within Carolina wrens specifically, suggesting potential mechanisms generating these carry-over effects. Offspring body mass and fledging age are often predictive of post-fledging survival and recruitment. Thus, our results suggest that increasing temperatures may affect fitness in wild populations in species-specific ways, and induce life-history changes including the classic trade-off parents face between the size and number of offspring.
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Affiliation(s)
- Alexander J Mueller
- Department of Biological Sciences and Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, USA
| | - Kelly D Miller
- Department of Biological Sciences and Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, USA
| | - E Keith Bowers
- Department of Biological Sciences and Edward J. Meeman Biological Station, University of Memphis, Memphis, TN, USA.
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13
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Bowers EK, Jenkins JB, Mueller AJ, Miller KD, Thompson CF, Sakaluk SK. Condition-Dependent Begging Elicits Increased Parental Investment in a Wild Bird Population. Am Nat 2019; 193:725-737. [PMID: 31002567 DOI: 10.1086/702848] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The coevolution of parental supply and offspring demand has long been thought to involve offspring need driving begging and parental care, leaving other hypotheses underexplored. In a population of wild birds, we experimentally tested whether begging serves as a negatively condition-dependent signal of need or a positively condition-dependent signal of quality. Across multiple years, we supplemented nestling house wrens with food shortly after hatching and simultaneously manipulated corticosterone levels to simulate the hunger-induced increase in glucocorticoids thought to mediate begging. This allowed us to also test whether begging is simply a proximate signal of hunger. Days after supplementation ended, food-supplemented nestlings were in better condition than nonsupplemented nestlings and begged for food at an increased rate; their parents, in turn, increased provisioning to a greater extent than parents of nonsupplemented young, as begging positively predicted provisioning. Food-supplemented nestlings therefore attained above-average condition, which predicted their recruitment as breeding adults in the local population. Glucocorticoids increased begging in the short term, but this transient effect depended on satiety. Thus, glucocorticoids promoted begging as a proximate response to hunger, whereas the longer-term changes in nestling condition, begging, and food provisioning suggest that begging ultimately signals offspring quality to elicit increased investment, thereby enhancing offspring survival.
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