Patterns Of Parental Care Research Articles

Parental Responses to Changes in Costs and Benefits Along an Environmental Gradient

We evaluated the effects of dissolved oxygen on offspring survival, parental costs, and the pattern of parental care in Florida flagfish, Jordanella floridae (Cyprinodontidae). Specifically, we quantified (1) embryonic development and survival in the absence of parental care, (2) behavior of non-reproductive adults, and (3) behavior of parental males across a gradient in dissolved oxygen. Embryo developmental rates and survivorship increased with dissolved oxygen, with a relatively sharp increase in survival between medium and high oxygen treatments. Non-reproductive adults increased their frequency of aquatic surface respiration, reduced overall activity, and increased opercular beat rate as oxygen declined, suggesting increased costs of activity with reduced oxygen. Taking these cost measures together, costs appear to increase slowly as oxygen starts to decline and then increase sharply as conditions approach hypoxia. In contrast, parental effort increased gradually with dissolved oxygen. We conclude that the increase in care from low to medium oxygen primarily results from a sharp decline in physiological costs, whereas the continued increase in care from medium to high oxygen primarily results from an increase in offspring value. In addition, our results highlight that the benefits of fanning for offspring are not well understood and that they may increase with oxygen, contrary to what has been previously assumed.

Paternal care in the social and diurnal striped mouse (Rhabdomys pumilio): laboratory and field evidence.

Paternal care is rare in mammals, occurring mainly in carnivores and neotropical primates, in which the difficulties of long generation time and large individuals lead to small sample sizes. Here, the authors show that paternal care can be easily studied in the four-striped mouse (Rhabdomys pumilio) because (a) captive males show all the patterns of parental care as do females, with the obvious exception of nursing; (b) in the field, wild males act amicably toward juveniles and retrieve pups experimentally presented to them; (c) the striped mouse facilitates experimental approaches in captivity because it has a short generation period and can be kept in large numbers; and (d) the striped mouse is diurnal, not only making observations in captivity easier but also enabling direct observations in the field.

Sex differences in razorbill (Family: Alcidae) parent–offspring vocal recognition

In this study we examines how a pattern of parental care may result in a sex bias in vocal recognition. In Razorbills (Alca torda), both sexes provide parental care to their chicks while at the nest, after which the male is the sole caregiver for an additional period at sea. Selection pressure acting on recognition behavior is expected to be strongest during the time when males and chicks are together at sea, and as a result, parent–offspring recognition was predicted to be better developed in the male parent, that is, show a paternal bias. In order to test this hypothesis, vocal playback experiments were conducted on breeding Razorbills at the Gannet Islands, Labrador, 2001. The data provide clear evidence of mutual vocal recognition between the male parent and chick but not between the female parent and chick, supporting the hypothesis that parent–offspring recognition is male biased in this species. In addition to acoustic recognition, such a bias could have important social implications for a variety of behavioral and basic life history traits such as cooperation and sex-biased dispersal.

Parental care and adaptive brood sex ratio manipulation in birds.

Under many circumstances, it might be adaptive for parents to bias the investment in offspring in relation to sex. Recently developed molecular techniques that allow sex determination of newly hatched offspring have caused a surge in studies of avian sex allocation. Whether females bias the primary brood sex ratio in relation to factors such as environmental and parental quality is debated. Progress is hampered because the mechanisms for primary sex ratio manipulation are unknown. Moreover, publication bias against non-significant results may distort our view of adaptive sex ratio manipulation. Despite this, there is recent experimental evidence for adaptive brood sex ratio manipulation in birds. Parental care is a particularly likely candidate to affect the brood sex ratio because it can have strong direct effects on the fitness of both parents and their offspring. We investigate and make predictions of factors that can be important for adaptive brood sex ratio manipulation under different patterns of parental care. We encourage correlational studies based on sufficiently large datasets to ensure high statistical power, studies identifying and experimentally altering factors with sex-differential fitness effects that may cause brood sex ratio skew, and studies that experimentally manipulate brood sex ratio and investigate fitness effects.

IN MEMORIAM: FRANK MCKINNEY, 1928–2001

Frank McKinney was born in Ballymena, Northern Ireland, on 23 October 1928, and died 12 June 2001, in St. Paul, Minnesota. He is survived by his wife of 38 years, Meryl, and his mother, Nin. Frank received his B.A. in Zoology from Oxford (1949) and his Ph.D. from Bristol (1953) before doing a post-doctorate with future Nobel laureate Niko Tinbergen at the Wildfowl Trust in Slimbridge. Twelve years as Assistant Director of the Delta Waterfowl Research Station in Manitoba brought him to a new hemisphere and taught him that administration was not his calling, so he moved on to the James Ford Bell Museum of Natural History at the University of Minnesota in 1963, where he remained as Curator of Ethology and Professor in the Department of Ecology, Evolution, and Behavior until retiring in 2000. He enjoyed a distinguished professional career as an inspiring teacher and ground-breaking researcher. A member of the AOU since 1955, he gained recognition as an Elective Member in 1960 and a Fellow in 1975, and was awarded the Brewster Award in 1994 for his many contributions to waterfowl social behavior. He was also a Fellow of the Animal Behavior Society. Frank enjoyed a worldwide reputation as the foremost authority on social behavior of dabbling ducks. He presented over 80 research talks and participated in dozens of symposia and workshops on topics ranging from wildlife management to sperm competition to the behavioral adaptations of southern hemisphere waterfowl. He was a fixture at AOU, Animal Behavior Society, International Ethological Conferences, and International Ornithological Congresses. Many of his comparative and experimental studies on ducks were conducted in special flight pens he designed and built at the Cedar Creek Natural History Area just north of the twin cities, but he also did field studies of free-living ducks in Canada, South Africa, Australia, New Zealand, and the Bahamas. Frank sought (and identified) many of the key selection pressures likely to have shaped the social behavior patterns of dabbling ducks, especially their remarkable diversity of territorial behavior, promiscuity, and parental care patterns. Due to my own fortuitous timing, I noticed that Frank actually had two major research careers. Initially trained as a classical comparative ethologist, he learned the disciplines of meticulous observation and objective description. To Frank, the behaviorist's first duty was to know the animal under study as well as possible and the only way to do that was to put in countless hours of quiet observation. There was nothing flashy, hyped, or pretentious about him. He prided himself on doing careful, indeed cautious work. During the 1950s and 1960s, Frank was oriented mainly on the macroevolutionary aspects of duck social signals and other behavior patterns, which he studied tirelessly with both captive and free-living subjects. But by the late 1960s, some of his excitement with that approach had begun to fade and Frank later admitted to me that he had gone a bit flat. So he reinvented himself. The centennial commemoration of Darwin's book on selection (Campbell 1972) set Frank off in a series of new directions. The concept now called sexual conflict (basically, recognition of the fact that males and females often have noncongruent fitness interests) immediately cast doubt on the old notion of pairbonding. Bob Trivers's unexpected proposal that the two sexes could almost be regarded as belonging to different species recast courtship as a process of mutual assessment and simultaneously sparked fresh interest on the practice of extrapair matings, consensual and otherwise, for which ducks were especially puz-

MALE-FEMALE DIFFERENCES IN PARENTAL CARE IN MONOGAMOUS CRESTED AUKLETS

Abstract We studied patterns of parental care in Crested Auklets (Aethia cristatella), a monogamous seabird, for three breeding seasons (1996–1998) in the Aleutian Islands, Alaska, using radio-telemetry. In 1996, we found no sexual differences in parental care, low breeding site attendance rates, and reduced occurrences of copepods in food samples delivered to chicks, suggesting that food availability may have been low. In 1997 and 1998, we found significant differences in parental care between males and females, particularly early in the chick-rearing period: males attended and brooded their single chick 75% and 90% longer than females, while females provisioned 33% and 36% more often than males, respectively. We also found significant differences between prey types delivered to chicks by males and females for these two years. Males brought in 30% more euphausiids, a relatively large pelagic crustacean, than females, whereas females brought in 36% more copepods, a smaller crustacean, than males; however,...

Female nest defense in a coral-reef fish, Dascyllus albisella , with uniparental male care

Intraspecific variation in the patterns of parental care has been observed in a variety of animals; however, the possibility of parental care by a non-caregiving parent of uniparental species has not been thoroughly explored. In the coral-reef damselfish, Dascyllus albisella, only males normally exhibit parental care. In this study, we examined the response of females of this species to egg predators after experimental male removal and an elevated level of egg predation, at two small patch reefs (reefs 1 and 2) in Hawaii. We tested theoretical expectations that a nest was defended only by females which had spawned in the nest, and that larger females had a higher likelihood of defense than smaller females. A nest was defended against egg predators more frequently by females that had spawned in that nest than would be expected by chance. Not all females that had spawned in a given nest participated in defense. There was a positive association between female body length and the likelihood of defense at reef 2, but not at reef 1. Within a set of females that had spawned in the same nest during the same nesting cycle, defending females had larger body lengths than non-defending females at reef 2 but not at reef 1. Lack of association between female size and likelihood of defense at reef 1 was unexpected, but may correlate with the smaller average female size and smaller size differences among females on that reef.

Female‐biased dispersal, low female recruitment, unpaired males, and the extinction of small and isolated bird populations

Small and isolated populations are usually assumed to be at a high risk of extinction due to environmental or demographic stochasticity, genetic problems, or too little immigration. In birds, natal dispersal is usually female‐biased, but the consequences of such a pattern on vulnerability to extinction of isolated populations has not received much attention before. In this paper I derive predictions as to how female‐biased natal dispersal may differentially affect the extinction risk of populations and species with contrasting distributions, migratory behaviours, life histories and mating systems. Female‐biased dispersal will lead to male‐biased sex ratios in small, isolated or fragmented populations, in particular because recent research has shown that females often have a limited ability to search for mates and may therefore effectively be lost from the breeding population if they disperse into areas empty of conspecifics. I reviewed published studies on birds and found that a high proportion of unpaired males is common in isolated populations or populations in small habitat fragments. Dispersal of females may therefore increase the vulnerability to extinction of small or isolated populations, or populations at the periphery of a species’ distribution range. I also predict that vulnerability to extinction should be greater for migratory than for resident species and greater for short‐lived than for long‐lived species because of differences in the time available for females to locate unpaired males. Further, extinction risk may also be greater for birds than for mammals due to differences in which sex disperses and patterns of parental care. Finally, mating system will also affect vulnerability to extinction when natal dispersal leads to biased sex ratios. I review available evidence for these predictions (e.g. songbird declines in North America) and discuss implications for conservation.

The Evolution of Parental Care in Freshwater Leeches

The life-history strategies of a selection of the most common European freshwater leeches (Euhirudinea) are described. On the basis of this information and results from the literature, the probable phylogenetic development of parental care in the Euhirudinea is reconstructed. The jawless worm leeches (Erpobdellidae) secrete a protective cocoon, cement it to the substrate and sometimes ventilate it before they leave the egg capsules. This behaviour represents the most ancient state in leech evolution. Members of the jawed Hirudinidae deposit desiccation-resistant cocoons on land. All known Glossiphoniidae (leeches equipped with a proboscis) have evolved the habit of brooding the eggs and young. These unique parental care patterns within one family of extant freshwater leeches can be arranged schematically in a series of increasing complexity which may reflect the evolution of brooding behaviour. Glossiphoniid leeches of the genus Helobdella, which have a world-wide distribution, display the most highly developed parental care system: they not only protect but also feed the young they carry. This results in the young being much larger when they leave the parent and, presumably, in higher subsequent survival. Isolated cocoons of all aquatic leeches are rapidly destroyed by predators, primarily water snails. In erpobdellids (but not glossiphoniids, which protect the cocoons) a large portion of the cocoons are lost due to predatory attacks. We conclude that the major selective pressure driving the evolution of parental care in leeches may have been predation on eggs and juvenile stages.

Avian Life Histories: Is Extended Parental Care the Southern Secret?

SummaryMost theories of life history evolution have been based on demographic studies from cool temperate regions of the northern hemisphere, where many birds either migrate to avoid severe winters or suffer high mortality if they stay. Life histories of species living in tropical and southern temperate regions are typified by smaller clutches, multiple nesting attempts, high levels of nest predation, and high adult survival. Hypotheses explaining the evolution of these different patterns invoke differences in food availability, nest predation or mortality. The difficulty in deciding between different hypotheses lies in the lack of information about the breeding biology of species living in the southern hemisphere. One aspect of life history variation that has received little attention is the survival of juveniles, which requires intensive study of known individuals, difficult in all but sedentary species. Extended parental care may promote the survival of juveniles, and thus counteract the effects of smaller clutches. I concentrated on the Passeriformes and reviewed the Time to Independence and the length of time for which juveniles were allowed to stay in the family group or territory after fledging. Species of the northern temperate regions show patterns in which young associate with their parents for only a short time before having to fend for themselves, less than one month in a majority of species. This contrasts with patterns of parental care in species of the tropics and southern temperate regions, in which Time to Independence is generally at least one month, and a majority of species remained with their parents for at least three months. I suggest that by increased investment in a few young, total reproductive effort is reduced, which may contribute to higher adult survival. The need for management to take account of life history attributes is emphasised.

Trade-off between mating opportunities and parental care: brood desertion by female Kentish plovers.

Why do some parents care for their young whereas others divorce from their mate and abandon their offspring? This decision is governed by the trade-off between the value of the current breeding event and future breeding prospects. In the precocial Kentish plover Charadrius alexandrinus females frequently, but not always, abandon their broods to be cared for by their mate, and seek new breeding partners within the same season. We have shown previously that females' remating opportunities decline with date in the season, so brood desertion should be particularly favourable for early breeding females. However, the benefits are tempered by the fact that single-parent families have lower survival expectancies than those where the female remains to help the male care for the young. We therefore tested the prediction that increasing the value of the current brood (by brood-size manipulation) should increase the duration of female care early in the season, but that in late breeders, with reduced remating opportunities, desertion and thus the duration of female care should be independent of current brood size. These predictions were fulfilled, indicating that seasonally modulated trade-offs between current brood value and remating opportunities can be important in the desertion decisions of species with flexible patterns of parental care.

Phylogenetic analysis of the Sphaeriidae (Mollusca: Bivalvia) based on partial mitochondrial 16s rDNA gene sequences

Abstract. We have constructed molecular phylogenetic trees for members of the Sphaeriidae in order to test proposed generic level relationships, and to reconstruct the evolutionary pattern of parental care, in this exclusively freshwater family of heterodont bivalves. An ∼480 nucleotide fragment of the mitochondrial large ribosomal subunit (16s rDNA) was sequenced for 4 corbiculid outgroups in addition to 19 sphaeriid ingroup taxa. Ingroup species were obtained from North and South America, Europe, and Australasia and included representatives of the main sphaeriid genera. Our analyses support four primary conclusions: 1) the Sphaeriinae are robustly monophyletic with respect to Eupera platensis; 2) the genus Pisidium is paraphyletic and P. sterkianum is sister to the 17 other sphaeriine taxa in our dataset; 3) synchronous brooding is the ancestral reproductive pattern in the Sphaeriinae; 4) the sequential brooders form a clade in which Musculium taxa are monophyletic and nested among lineages of Sphueriunz. Our gene trees reveal an evolutionary progression in parental care complexity from the relatively simple pattern in the Euperinae, to the origin of brood sacs and of extraoogonial embryonic nutrition in the common ancestor of the Sphaeriinae, and ultimately to the development of sequential brooding in Sphaerium/Musculium taxa.

Timing of oviposition and reproductive skew in cobreeding female burying beetles (Nicrophorus vespilloides)

Burying beetles (genus Nicrophorus) are known for their elaborate parental care. Two or more conspecific females may reproduce on the same carcass, especially when the carcass is large. Here we present the results of experiments in which we observed patterns of larval hatching and parental care in unmanipulated cobreeders, manipulated hatching synchrony between cobreeders, and compared patterns of oviposition in cobreeding and single females. Our results show that in these cobreeding associations, one of the females may or may not monopolize the carcass during the period of larval hatching. We present evidence that in either case, infanticide based on temporal cues constitutes an important proximate mechanism underlying the observed reduction in average reproductive success in cobreeding females. Females with higher synchrony (i.e., greater overlap between their oviposition patterns) produce larger broods with lower reproductive skew. Cobreeding females oviposit later and less synchronously than single breeders. Such delayed oviposition may reduce the risk that a female’s larvae fall victim to cannibalistic acts committed by her cobreeder or maximize her own opportunity to selectively kill her cobreeder’s larvae. Key words: burying beetles, cannibalism, communal breeding, infanticide, kin recognition, Nicrophorus, parental care, reproductive competition, reproductive skew. [Behav Ecol 11:357–366 (2000)] R eproductive competition is ubiquitous among communally breeding animals. When several conspecific females share a breeding site, as is the case in some vertebrates (‘‘joint nesting’’ or ‘‘communal breeding’’) as well as in some primitively social or eusocial insects (polygyny), young in the communal nest may compete for food. In this situation, females may increase their individual reproductive success by destroying their cobreeders’ eggs or young while sparing their own. Such selective infanticide requires the perpetrator to discriminate between her own offspring and those of cobreeders. One simple mechanism that can enable such discrimination is a temporal switch (Elwood, 1994), sometimes referred to as a ‘‘change in parental state’’ (Rosenblatt and Siegel, 1983), which is possibly mediated by hormonal changes triggered by important reproductive events (‘‘state-dependent cues’’; Elwood, 1991). Selective infanticide may result if the individual shows infanticidal behavior toward young at a time at which it is likely to encounter unrelated offspring, and parental, non-infanticidal behavior at a time when it is likely to encounter its own (Elwood, 1994). Examples include many bird species with intraspecific brood parasitism or communal breeding, in which females remove eggs from the nest throughout the prelaying period (i.e., until they have laid their first egg) (e.g., Emlen and Wrege, 1986; Macedo and Bianchi, 1997; Moller, 1987; Mumme et al., 1983; Stouffer et al., 1987; Vehrencamp, 1977), and males of many mammalian species that exhibit infanticidal behavior toward the young of females with whom they have not mated or cohabited long enough for the young to be the males’ own offspring (see Hrdy and Hausfater, 1984,

DNA Fingerprinting in Minyobates minutus, the Minute Poison Frog

DNA fingerprinting has become a widely used technique in the study of ecology and evolution (e.g., Parker et al., 1998). However, this technique has rarely been used in research on anurans (e.g., D'Orgeix and Turner, 1995). Here we present DNA fingerprinting data from a study of the minute poison frog, Minyobates minutus, in Panama. The purpose of this study was to investigate whether commonly used DNA fingerprinting probes are useful in investigating genetic relatedness in a wild population of poison frogs. DNA fingerprinting could be a particularly useful tool for research on the ecology and evolution of poison frogs, because these frogs exhibit complex patterns of parental care involving high levels of parental investment (Wells, 1981; Weygoldt, 1987; Zimmermann and Zimmermann, 1988). Such high levels of parental investment make issues of paternity and maternity of critical interest to those investigating the evolution of parental care in members of the family Dendrobatidae (Summers and Earn, 1999). Furthermore, the fact that tadpoles in this group are highly cannibalistic (e.g., Summers, 1990; Caldwell and Araujo, 1998), and frequently placed together in small pools, such as bromeliad tanks or Heliconia leaf axils (e.g., Summers and Amos, 1997; Caldwell and Araujo, 1998), makes knowledge of kinship particularly valuable for investigations of kin recognition and its functional significance (Pfennig, 1997). The clutch size of Minyobates minutus appears to be small, consisting of two eggs on average. Survival rates of clutches in the field are unknown, but once the developing embryo reaches the tadpole stage it is carried to phytotelmata and deposited by a male nurse frog (pers. obs.). These phytotelmata are typically found in bromeliads, which are abundant at the study site. Collections were made in the Nusagandi Biological Reserve, Comarca de San Bias, Republic of Panama. Ten males carrying tadpoles were collected to serve as references for bandsharing values between parents and offspring. Males in this species typically carry a single tadpole on their back. An additional 17 adults were collected in order to investigate levels of bandsharing between putatively unrelated individuals. Comparisons were made among these individuals and among adults or tadpoles from the reference group, for a total of 21 comparisons of putatively unrelated individuals. Each individual was compared only once, and comparisons were made between individuals that were run on the same gel (within four lanes of each other). Frogs and tadpoles were instantaneously frozen in liquid nitrogen in the field, and later stored at -70 degrees in the Smithsonian Tropical Research Institute's molecular evolution laboratory in Panama City, Panama. Specimens were later transported in a dry shipper (liquid nitrogen container) to the molecular ecology laboratory at Queen's University. DNA was extracted from the samples using standard phenol/chloroform methods (Summers et al., 1999): Approximately 0.2 g of leg muscle tissue was homogenized in 500 ,pl of Ix AB (Applied Biosystems) lysis buffer in a 1.5 ml tube and mixed on a rotating wheel overnight at 37 C. The following day 25 units of proteinase K were added to each of the samples, which were mixed overnight on a rotating wheel at 37 C. The following day an equal volume of buffered, equilibrated phenol was added to each sample and shaken for 2-3 min by hand, then centrifuged at 13,000 rpm in a clinical centrifuge. The aqueous (top) layer was removed and transferred to a new tube, and the process was repeated with PCI (phenol: chloroform:isoamyl alcohol: 25:24:1) and then with chloroform: isoamyl alcohol (24:1). Next 50 pLI of 3M sodium acetate (pH 3.5) was added to the resulting supernatant and mixed gently, followed by the addition of two volumes of 95% ethanol. This mixture was

When do Males Sing Songs? Costs and Benefits of Singing during a Breeding Cycle.

To maximize their reproductive success, male birds have to acquire females, ensure their paternity, and increase the survival of their offspring. Males therefore allot their reproductive efforts to several activities during the nesting cycle, because there are trade-offs among the reproductive behaviours. In the Great Reed Warbler, Acrocephalus arundinaceus, there is a negative correlation between singing frequency and intensity of mate guarding, and between singing frequency and male feeding rate. Furthermore, male Great Reed Warblers adjust the time of singing by estimating the risk of paternity loss and abundance of potential secondary mates. In the Bush Warbler, Cettia diphone, males vigorously sing throughout the breeding season, which may be due to frequent female remating due to nest predation, resulting in a continuous source of potential mates for males. Thus, the timing of male singing is influenced by the costs and benefits of singing, which are related to other reproductive activities. Therefore, to understand singing activity, the social and ecological circumstances of the species should be considered, especially the occurrence of extra-pair fertilization, the pattern of parental care, the pattern of female arrival at the breeding area, and successiveness of pairbonds.

Multiple patterns of parental care

Many animals show multiple patterns of parental care, where more than one of the four basic patterns (biparental care, uniparental care by males or females, or no care) is present within a single population during a single breeding season. We consider three reasons for the existence of multiple patterns of parental care: (1) mixed-strategy behaviours; (2) time-dependent behaviour with parents changing their care decision during the breeding season; and (3) quality differences between individuals leading to different care decisions being made depending on the qualities of both parents. The basic framework we use to investigate these is a two-stage game-theoretical model, and we highlight the importance of including feedback between the parental care decisions made by population members and the probability that a deserting individual will find a new mate. Including this feedback may introduce a nonlinear dependence of the fitness payoffs on the frequencies with which the pure strategies (‘care’ and ‘desert’) are played by each of the sexes. This can have important consequences for the existence of evolutionarily stable strategies (ESSs). For example, mixed-strategy ESSs may exist (an outcome forbidden if the feedback is not included) and, in one model, the feedback also prevents uniparental care by either sex from being evolutionarily stable. We also point out that decisions made by animals without dependent offspring can have important consequences for observed parental care behaviour.

Individual differences in parental care and behaviour profile in the convict cichlid: a correlation study

We examined whether individual differences in patterns of parental care relate to individual differences in situations involving novelty, risk and aggression in the convict cichlid, Cichlasoma (Archocentrus) nigrofasciatum . Individual differences in situations of novelty and risk could be summarized along two axes: Freezing versus Activity and Activity-Inspection versus Freezing. However, these factors were not independent and formed a single higher-order dimension of general activity. Parental locomotor activity was negatively correlated with the Freezing versus Activity factor in females. Males that did little brood provisioning tended to be less active in the presence of a novel fish. Individuals that spent more time near their offspring at late brood stages were less inhibited in behavioural tests. Furthermore, extreme assortative mating by body size was found (rS=0.91). The cichlids also spawned assortatively by the factor Freezing versus Activity and by the general activity factor (rS≥0.49), but not by the factor Activity- Inspection versus Freezing or by aggressiveness.

Brood desertion in Kentish plover: sex differences in remating opportunities

To understand the evolution of parental care, one needs to estimate the payoffs from providing care for the offspring and the payoffs from terminating care and deserting them. These payoffs are rarely known. In this study we experimentally estimated the rewards from brood desertion in a species that has a variable pattern of parental care. In particular, either the female or the male parent may desert the brood in Kentish plover Charadrius alexandrinus, so some broods are attended by one parent of either sex, whereas in other broods both parents stay with the brood until the chicks fledge. We created single males and single females by experimentally removing the other parent and the clutch. The expected remating time of males was significantly higher (median: 25.4 days) than that of the females (5.3 days, p , .0001). The expected remating time tended to increase over the breeding season in both sexes, although the increase was significant only in females. The new nest of remated males was closer to their previous territory (mean 6 SE, 46 6 8 m) than that of the remated females (289 6 57 m, p , .001). Hatching success of new nests was not different between remated males and females. Our results demonstrate that the remating opportunities are different for male and female Kentish plovers and these opportunities vary over the season. We propose that the remating opportunities were influenced by the male-biased adult sex ratio and the seasonal decrease in the number of breeders. However, we stress that measuring remating times is a more direct measure of mating opportunities than calculating the operational sex ratio.

On the evolutionary pathway of parental care in mouth–brooding cichlid fishes

Evolutionary theory predicts that differences in parental care patterns among species arose from interspecific differences in the costs and benefits of care for each sex. In Galilee St Peter9s fish, Sarotherodon galilaeus (Cichlidae), male care, female care and biparental care all occur in the same population. We exploit this unusual variability to isolate conditions favouring biparental versus uniparental mouth–brooding by males or females. We first review a game–theoretic model of parental care evolution, predictions of which we test experimentally in this paper. Manipulations of the operational sex ratio show that males and females desert their offspring more frequently when the costs of care are high (in terms of lost mating opportunities). Breeding trials with males of different sizes show that small fathers desert more frequently than large fathers. We attribute this to the associated difference in the fitness benefit of biparental care relative to female–only care. Our experimental results confirm that in St Peter9s fish the probability of caring is determined facultatively according to current conditions at each spawn. The experiments and model together suggest that interspecific variation in remating opportunities and clutch size may be responsible for differences in care patterns within the sub–family Tilapiini. Our results support the hypothesis that biparental mouth–brooding was the ancestral state of both male and female uniparental mouth–brooding in cichlid fishes.

Brood division in birds in relation to offspring size: sibling rivalry and parental control

In some altricial birds with biparental care, it is the female, and in others the male, that provides more food to the smallest offspring within the brood. Many hypotheses have been proposed to account for such puzzling patterns of parental care. A parsimonious explanation is that no difference exists between the parents in priority of care but that differences arise simply from sibling rivalry, with dominant chicks trying to position themselves closest to the parent that provides most care (the sibling rivalry hypothesis). A refinement of the idea is that parents use the way they approach the chicks to counter selfish offspring and in this way control allocation of care (the parental approaching hypothesis). A comparison across species suggested that female care of the smallest chick within a brood is the ancestral and most common pattern. However, strong variation exists within single populations. In one species, the American robin,Turdus migratoriusthe sibling rivalry hypothesis and the parental approaching hypothesis were both supported because in broods where males provided more care than females, the largest chick was predominantly fed by the male whereas the smallest chick was predominantly fed by the female. When the male provided less care than the female, an opposite result was found. The same patterns of allocation of care also seemed to exist when chicks were quite immobile just after having left the nest and when their positions were experimentally controlled, suggesting parental control.