The effects of helpers in cooperatively breeding purple gallinules

Summary The effects of helpers in a population of cooperatively breeding purple gallinules (Porphyrula martinica) were examined. All young birds past the age of 2 months helped feed and protect subsequent broods of chicks and participated in territorial defense. Most helpers remained on their natal territories for approximately 1 year. The number of helpers varied both among and within breeding groups. Clutch production and chick survival were related positively to the number of helpers in the group. The increase in chick survival was independent of several measures of territory quality. Helpers possibly aided chick survival by provicing extra food for the chicks and decreasing predation risk. Helpers were necessary in order for a breeding pair to keep a territory long enough to produce more than one clutch of eggs. A change in the number of helpers (increase or decrease) often was followed by a similar change in territory size. These results suggest that purple gallnule helpers can increase the reproductive success of the breeding group and may be vital for the continued maintenance of a breeding territory.     

Genetic evidence for monogamy in the cooperatively breeding red-cockaded woodpecker

We examined the genetic relationship among putative parents, offspring, and helpers in 224 red-cock-aded woodpeckers (Picoides borealis) from the Sandhills of North Carolina. Comparison of DNA similarity with a pedigree constructed from 3,823 individually-marked birds observed from 1979 to 1992 provided verification of observed relatedness in the sampled population (R ² = 0.87, df = 14, P < 0.001). In this population, breeding pairs may or may not have helpers, most of which are males that remain on their natal territory. Our sample included helpers assisting their parents, helpers assisting a related male and an unrelated female, and helpers assisting an unrelated pair. Band by band comparison and examination of similarity among DNA profiles indicated that all offspring from non-helped nests were sired by their putative parents (n = 28 families). Similarly, all but one offspring in helped nests were also sired by their putative parents (n = 16 families). In the exceptional case, the offspring evidently was sired by a male external to the group. Analysis of similarity values supported the conclusion that matings by helpers or extra-group males are rare or non-existent. Our results indicate that in this species advantages gained by individuals remaining on their natal territories as helpers do not generally include siring offspring. Correspondence to: S. Haig     

Parental facilitation: parent-offspring relations in communally breeding birds

Summary A view of parent-offspring relations is developed that stresses an increased role for mutualism and tolerance rather than conflict in evolutionary trends toward sociality. For example, in Aphelocoma jays, parental tolerance of offspring increases from asocial to social species, contrary to what parental manipulation or parent-offspring conflict models have suggested. A simple model is presented in which parents can leave more grand-offspring while having fewer offspring through a mutualistic relationship between parent and offspring. Consistent with the model are the following observations: (1) At the extreme of sociality, in Mexican jays, A. ultramarina, both sexes commonly inherit their natal territory, thus retaining productive territories largely under control of genotypes that tolerate persistence of young in the territory. Sons and daughters may breed on their natal territory in the presence of their mothers and presumed fathers. (2) Jays banded as nestlings in the study area achieved higher reproductive success when breeding on their natal territory than those that moved to other territories. It is hypothesized that plural breeding can evolve as an extension of the trend leading to singular breeding via a non-altruistic reduction in the number of offspring per parent. The concept of parental facilitation may prove to be important for many highly social types of animals, including insects, birds and mammals.     

Genetic evidence for monogamy in the cooperatively breeding red-cockaded woodpecker

We examined the genetic relationship among putative parents, offspring, and helpers in 224 red-cockaded woodpeckers (Picoides borealis) from the Sandhills of North Carolina. Comparison of DNA similarity with a pedigree constructed from 3,823 individually-marked birds observed from 1979 to 1992 provided verification of observed relatedness in the sampled population (R ² = 0.87,df = 14,P<0.001). In this population, breeding pairs may or may not have helpers, most of which are males that remain on their natal territory. Our sample included helpers assisting their parents, helpers assisting a related male and an unrelated female, and helpers assisting an unrelated pair. Band by band comparison and examination of similarity among DNA profiles indicated that all offspring from non-helped nests were sired by their putative parents (n = 28 families). Similarly, all but one offspring in helped nests were also sired by their putative parents (n = 16 families). In the exceptional case, the offspring evidently was sired by a male external to the group. Analysis of similarity values supported the conclusion that matings by helpers or extra-group males are rare or non-existent. Our results indicate that in this species advantages gained by individuals remaining on their natal territories as helpers do not generally include siring offspring. Correspondence to: S. Haig     

Correlates of group size in a cooperatively breeding cichlid fish (Neolamprologus pulcher)

Neolamprologus pulcher, a cooperatively breeding cichlid fish from Lake Tanganyika, lives in permanent social groups comprising one breeding pair and helpers of both sexes. Variation in group size (1-14 helpers) provides an opportunity to investigate factors that affect how many helpers remain in a group and in turn how group size affects reproductive success. This field study showed that larger groups live in larger territories with more shelter. Group size was more strongly correlated with territory quality than with breeder size. Experimental enhancement of territory quality did not affect group size but group size decreased when territory quality was reduced. Breeders living in a large group benefit because such individuals feed more often and have lower workloads and greater reproductive success. Helpers in larger groups also fed more frequently but did not have lower workloads. This is one of the first experimental studies to examine the factors influencing group size in cooperative breeders.     

Multiple paternity in the cooperatively breeding fish <Emphasis Type="Italic">Neolamprologus pulcher</Emphasis>

In cooperative breeders, mature males may compete for fertilizations. In this study, we measured the degree of multiple paternity in a natural population of a cooperatively breeding fish. Neolamprologus pulcher (Perciformes: Cichlidae) is a highly social cichlid endemic to Lake Tanganyika. We used highly variable microsatellite loci to survey 12 groups with an average number of 10.6 brood care helpers per group and a total of 43 offspring (mean 3.6 per brood). In 11 of 12 groups, all young were assigned to the dominant female. The dominant male sired all offspring in three groups, part of the offspring in four groups, and in five groups, he had no paternity at all. In total, 44.2% of young were not fathered by the current male territory owner. Multiple paternity was found in 5 of 12 broods (41.7 %), with 8 of 35 young (22.9 %) being sired by males other than the respective territory owners. This is an exceptionally high rate of extra-pair paternity among cooperatively breeding vertebrates. Neither helpers present in these territories during collection nor neighbouring males were unequivocally assigned to have sired these extra-pair young. However, behavioural observations suggest that male helpers may have produced these young before being expelled from the territory in response to this reproductive parasitism. We discuss these results in the light of reproductive skew theory, cooperative breeding in vertebrates and alternative reproductive tactics in fish.     

Relatedness, polyandry and extra-group paternity in the cooperatively-breeding white-browed scrubwren (Sericornis frontalis )

We used DNA fingerprinting to examine the genetic parentage and mating system of the cooperatively breeding white-browed scrubwren, Sericornis frontalis, in Canberra, Australia. Our analyses revealed a remarkable variety of mating tactics and social organization. Scrubwrens bred in pairs or multi-male groups that consisted of a female and two or more males. Females were always unrelated to the pair male or alpha (dominant) male. Among multi-male groups we found three different mating tactics. Firstly, when alpha and beta (subordinate) males were unrelated, they usually shared paternity in the brood. This resulted in both males gaining reproductive benefits directly. Secondly, when beta males were not related to the female but were related to the alpha males, beta males sired offspring in some broods. In this situation, beta males gained reproductive benefits both directly and potentially indirectly (through the related alpha male). Thirdly, when beta males were related to the female or both the female and alpha male, they remained on their natal territory and did not sire any offspring. Thus beta males gained only indirect reproductive benefits. Overall, when group members were related closely, the dominant male monopolized reproductive success, whereas when the members were not related closely the two males shared paternity equally. This positive association between monopolization of reproduction and relatedness is predicted by models of reproductive skew, but has not been reported previously within a single population of birds. Other cooperatively breeding birds with both closely related and unrelated helpers may show a similar variety of mating tactics. Finally, we found that extra-group paternity was more common in pairs (24% of young) than in multi-male groups (6%), and we discuss three possible reasons for this difference. Received: 21 May 1996 / Accepted after revision: 14 December 1996     

Cooperative breeding by the Galápagos mockingbird,Nesomimus parvulus

Summary The costs and benefits of helping behavior were analyzed for 36 pairs of the Galápagos mockingbird, Nesomimus parvulus, and their associates. Helping at the nest is usually done by sons or males suspected to be offspring of the breeders. Costs and benefits to breeders were assessed by comparison of pairs with and without helpers, and costs and benefits to helpers were assessed by comparison of birds which help and those which establish themselves as novice breeders.Helping behavior benefits breeders by increasing fledging success and by reducing the adult energy load in territory defense and feeding of nestlings. Breeders assisted by helpers may also benefit by decreased nest predation. Helpers enhance their inclusive fitness by helping, and gain directly by increasing their chances of securing a territory. Helpers do not appear to gain any fitness advantage from the experience of assisting, nor do they increase their survivorship by remaining on natal territory.Ecological and demographic features such as saturated territories and low territory turn-over rates due to high adult survival may be primarily responsible for the evolution of the helping behavior, with kinselection reinforcing it. Associated features of this system are a male-biased population sex ratio, a greater energetic benefit to breeding males than to breeding females in having helpers, earlier dispersal and breeding by females than by males, and much more frequent helping by males than by females. These are interpreted as consequences of brothersister aggression that indirectly minimizes the chances of inbreeding.     

Intra-group relatedness affects parental and helper investment rules in offspring care

In any system where multiple individuals jointly contribute to rearing offspring, conflict is expected to arise over the relative contributions of each carer. Existing theoretical work on the conflict over care has: (a) rarely considered the influence of tactical investment during offspring production on later contributions to offspring rearing; (b) concentrated mainly on biparental care, rather than cooperatively caring groups comprising both parents and helpers; and (c) typically ignored relatedness between carers as a potential influence on investment behavior. We use a game-theoretical approach to explore the effects of female production tactics and differing group relatedness structures on the expected rearing investment contributed by breeding females, breeding males, and helpers in cooperative groups. Our results suggest that the breeding female should pay higher costs overall when helpful helpers are present, as she produces additional offspring to take advantage of the available care. We find that helpers related to offspring through the breeding female rather than the breeding male should contribute less to care, and decrease their contribution as group size increases, because the female refrains from producing additional offspring to exploit them. Finally, within-group variation in helper relatedness also affects individual helper investment rules by inflating the differences between the contributions to care of dissimilar helpers. Our findings underline the importance of considering maternal investment decisions during offspring production to understand investment across the entire breeding attempt, and provide empirically testable predictions concerning the interplay between maternal, paternal and helper investment and how these are modified by different relatedness structures.     

Cooperation in breeding by nonreproductive wrens: kinship,reciprocity, and demography

Summary Stripe-backed wrens (Campylorhynchus nuchalis) often live as adults in large groups on permanent, communally defended territories. Nonbreeding adults cooperate in rearing the young of a single breeding pair; this aid substantially increases the reproductive success of the breeders. In a 6-year study in Venezuela of a completely colorbanded population of 25–30 groups, most adults participated in breeding only as helpers and priority to breeding status was strictly age-determined. Detailed behavioral observations at breeding nests with nestlings showed that, in a sample of 100, helpers nearly always contributed as much to the care of young as breeders. Further, aid-giving does not vary systematically with relatedness of ycung to helpers or with probability of future reciprocation by young. Young being raised are most often at least half siblings of helpers, but seldom return aid to adults that helped raise them. Even adopted helpers collaborate fully. Patterns of demography and dispersal show slow turnover of breeders, delayed reproduction, and a viscous population structure.Application of Hamilton's condition for selection for aid-giving reveals that most individuals in this population can maximize inclusive fitness in the first 2 years by helping instead of breeding. Variation in helping effort and in age of first breeding is related to variation in natal group size and competition resulting from variable demographic neighborhoods in different years or in different parts of the population. Because reciprocation in the form of specific alliance formation among nonreproductives is uncommon, nonspecific reciprocity between cohorts and kin selection account well for the observed pattern of age-dependence in first breeding. Nondiscriminating helping in this population is associated with stable monogamous pair boncs, stable territory boundaries and group membership, strict seniortiy for breeding position, high viscosity and consistent effectiveness of aid. Under these circumstances, very simple behavioral rules amounting to nearly automatic helping seem sufficient to confer critical inclusive fitness gain on helpers.     

Nepotistic access to food resources in cooperatively breeding carrion crows

Offspring delayed dispersal is the principal mechanism leading to formation of kin-based societies. It has been suggested that parents promote offspring philopatry by providing them with preferential access to the food resources of the territory and that parental tolerance may be affected by territory quality. However, few studies have addressed this hypothesis in kin-living vertebrate species. Here, we show that in cooperative breeding groups of carrion crows (Corvus corone corone) containing retained offspring and immigrants, dominant breeding males behaved nepotistically on an experimental source of food by (1) attacking immigrants with more frequency and intensity than offspring and (2) associating preferentially with their offspring on the feeding spot and sharing food with them. This parental facilitation allowed the offspring to spend more time feeding than higher-rank immigrants. We also found that a year-round experimental food supplementation neither increased breeding males’ tolerance nor relented the overall aggressiveness in the groups. This indicates that higher natal philopatry observed on fed territories compared to unfed ones is not a consequence of a more benign social environment. Rather, it suggests that offspring value territory resource wealth and adjust the timing of dispersal accordingly.     

Sociality and cooperative breeding of red-cockaded woodpeckers,Picoides borealis

Summary Thirty groups of red-cockaded woodpeckers (Picoides borealis) were studied from 1976–1982 to (1) determine the demographic structure of groups, (2) identify the role helpers play in reproductive activities, and (3) investigate the selective pressures promoting sociality and helping behavior. Groups had only 1 mated pair and 0–2 helpers. Approximately half of all groups had helpers and a given group had helpers some years but not others. Helpers, with rare exception, were males 1 or 2 years old and progeny of 1 or both members of the breeding pair. As a result of higher nestling survival, groups with helpers fledged significantly more young per year than unassisted pairs ( , SD=0.97,n=43 vs. , SD=1.01,n=50). Nesting success was also associated with size and quality of nesting period home range, but evidence suggested that the increased number of young fledged resulted directly from the action of helpers. There was a significant positive correlation between reproductive success and experience of breeding females among unassisted pairs but a significant negative correlation among pairs with helpers. In groups with experienced females, helpers were assisting both their mothers and fathers and, therefore, were related to the offspring on the average by 0.50. In groups with inexperienced females, helpers were assisting their fathers and unrelated females and were related to the offspring by 0.25. The red-cockaded woodpecker's unique habit of excavating nest and roost cavities in living pines and the extended period of time required for excavation may be an important ecological constraint that promotes the retention of helpers. Because helpers are related to the offspring they help rear, kin selection and gains in indirect fitness may provide a partial explanation of why red-cockaded woodpecker helpers help. However, the negative correlation between the efficacy of helping behavior and the helpers' relatedness to the offspring they help rear implies that helpers are least effective in producing offspring which would represent greatest gains to indirect fitness. This raises questions about the relative importance of kin selection and indirect fitness in the evolution of helping behavior among red-cockaded woodpeckers.     

Reproductive suppression and inbreeding avoidance in wild populations of co-operatively breeding meerkats (Suricata suricatta)

Meerkats live in co-operatively breeding familial groups in which reproduction is monopolised by a dominant pair of breeders. Offspring of the breeders are behaviourally subordinate, and typically remain in their natal group as sexually mature, non-breeding helpers. In this study, we investigated the proximate factors limiting subordinate reproduction. Evidence for reproductive suppression by dominants was investigated by comparing life history, behaviour and hormonal profiles of dominants and subordinates. Baseline levels of plasma luteinising hormone (LH) were significantly higher in dominant than in subordinate females. However, following an exogenous injection of gonadotrophin-releasing hormone (GnRH), both categories had comparable concentrations of circulating LH. There were no significant differences in pre- or post-GnRH challenge LH levels in dominant or subordinate males. Reproduction in both dominant and subordinate females rarely occurred in the absence of unrelated males. Given that groups typically comprise parents and offspring, lack of suitable mates emerged as the primary constraint on subordinate reproduction. When this constraint was removed, subordinates typically bred but at a lower rate than dominants. This difference in reproduction may be attributed to intrasexual competition manifested through direct interference by dominant females through subordinate evictions, infanticide and the abandoning of subordinate litters. We argue that differences in reproductive regulation within mammalian co-operative breeding systems may be explained by differences in the mating strategy (inbreeding versus outbreeding) and the probability that subordinates in obligate outbreeding species will encounter unrelated opposite-sex partners. Received: 19 April 2000 / Accepted: 17 July 2000     

Flexible helper structure as an ecological adaptation in the pied kingfisher (Ceryle rudis rudis L.)

Summary The pied kingfisher has two types of helpers at the nest: primary ones, helping their own parents, and secondary ones, helping birds other than parents. Primary helpers are always accepted by breeding pairs, secondary helpers only in poor environmental conditions where the time and energy budget of parents is not sufficient for rearing the offspring alone. Under these conditions, helpers increase the breeding success of pairs (Tables 2 and 3) by providing additional food for the young (Table 4). Thus the flexible helper structure can be seen as an ecological adaptation. It is argued that-originating from a skewed sex ratio and breeding in colonies-this adaptation evolved through the combined effects of individual and kin selection.     

Reproductive enhancement by helpers and an experimental inquiry into its mechanism in the bicolored wren

Summary As part of continuing studies of sociality in the wren genus Campylorhynchus we have been studying the bicolored wren — a facultatively cooperative breeder — for the past 6 years in the central Venezuelan savanna. Reproductive groups have ranged in size from 2 to 5. In one of our study populations, only about 15% of the groups contained helpers, and nearly all these contained only a single male helper (Fig. 2). In an adjacent population, the majority of groups contained helpers, and more than half of these contained several helpers of either sex. Territory size is, on average, much smaller in the latter population. In these populations the presence of a single helper is associated with a three-fold increase in reproductive success (Table 1). Additional helpers are not associated with further reproductive enhancement. Enhancement is chiefly due to an increased proportion of nest starts that eventually produce independent juveniles. This reproductive enhancement is not merely an epiphenomenon resulting from the presence of helpers on territories which are superior for other reasons, such as greater resource availability or the quality of particular parents. It is also not a function of the mean or variance in nestling feeding rate. Predator exclusion experiments, in which certan nests were artificially protected from terrestrial predators, suggested that the mechanism of reproductive enhancement was heightened effectiveness of nest defense. Helpers are usually nondispersers from the parental territory, and have always been found to be close relative of the nestlings that they assist in rearing.     

Is kin cooperation going on undetected in marine bird colonies?

In multitudinous breeding colonies, kin interactions could go unnoticed because we are unaware of the kinship among adults we observe. Evidence of cooperation and competition between close adult kin in a blue-footed booby colony was sought by analyzing patterns of natal dispersal and proximity of nests. Male and female recruits nested closer to their own natal sites than to their parents’ current sites. Males (only) dispersed less far when both parents were present than when no parent or one parent was present, but not selectively close to fathers versus mothers when these were divorced. Neither parental presence nor parental proximity affected breeding success of recruits of either sex. Although distances between the nests of simultaneously recruiting broodmates were unrelated to their sex, males dispersed 13.1 m less when a sister was present than when a brother was present. Neither sex was affected in its dispersal distance by the presence or hatching order/dominance of a broodmate. Neither sex was affected in its breeding success by the presence versus absence of a broodmate, although female success increased with proximity of their brothers. Parents and sisters may actively or passively help males establish their first territories near their natal sites and nearby brothers may help females in their first breeding attempts; otherwise, boobies do not influence each other’s natal dispersal and first breeding success. It appears that boobies do not nest selectively close to or far from their parents, offspring, or broodmates. Why there is apparently so little cooperation and altruism between close adult relatives in booby colonies is puzzling.     

Do helpers increase reproductive success?

Summary Although several different hypotheses have been proposed to explain the evolution of helping behavior, most are based on the assumption that helping enhances the reproductive success of recipient breeders. I tested this assumption by removal experiments in the cooperatively breeding Florida scrub jay (Aphelocoma c. coerulescens). This species lives in permanently territorial social units containing a single breeding pair and none to six nonbreeders, which are usually offspring of the breeding pair and which usually act as helpers by feeding the nestlings and fledglings produced by the breeding pair. Although experimental removals of non-breeders in 1987–1988 had no significant effect on breeder survival, egg production, or hatching success, experimental groups suffered higher rates of predation on nestlings (1987) and lower rates of fledgling survival (both years) than did unmanipulated controls. As a result, experimental groups produced an average of only 0.56 independent juveniles, compared to 1.62 young for controls. Analysis of the factors contributing to nestling and fledgling mortality indicates that helping behavior per se (i.e., the aid that nonbreeders provide to dependent young), not the mere presence of nonbreeders, was responsible for the greater reproductive success observed in control groups. Because survival rates of allofeeders (i.e., those nonbreeders that provisioned dependent young) were virtually identical to those of non-allofeeders, the costs of helping behavior in this species appear to be small. Furthermore, nonbreeders are more likely to provision dependent young within their social unit when those young are closely related. I therefore conclude that nonbreeders increase their indirect fitness by serving as helpers and that helping behavior in the Florida scrub jay is a trait that has current selective utility. It remains debatable, however, whether helping in this species is an adaptation that has been shaped by the process of natural selection.     

Reproductive success increases with degree of kinship in cooperative coalitions of female red howler monkeys (Alouatta seniculus)

Evaluation of evolutionary mechanisms proposed to promote cooperative behavior depends on the relative influence of the behavior on the reproductive success of individuals, the reproductive success of the group in which they interact behaviorally, and the degree of gene correlation among cooperators. The genetic relationship within cooperative coalitions of female red howler monkeys was examined for three populations with different densities and growth rates. Patterns of gene correlation change within coalitions is documented using data from the mitochondrial and nuclear genomes, and long-term census monitoring. Differences in fecundity and infant survivorship within and between groups of unrelated (rˉ=0) and related (rˉ≥ 0.25) females are compared. Females that emigrate from their natal groups form coalitions with other migrant females. These coalitions attempt to establish a territory and, once successful in producing offspring, exclude other females from feeding resources. Females in these coalitions had different mtDNA haplotypes and a genetically estimated mean r of 0, supporting demographic data on emigration patterns indicating that these females rarely have the opportunity to form coalitions with kin. Patterns of recruitment and rate of matriline development within social groups supported behavioral data indicating that females actively attempt to promote their own matriline as breeders over that of other females, and that some matrilines are more successful at this than others. Mean r among females was significantly higher in coalitions established as social groups for several generations (rˉ=0.44). In these groups, females all shared the same mtDNA haplotype, and mtDNA haplotype divergence was significantly higher between than within groups. Females in coalitions with kin had significantly higher reproductive success than females in unrelated coalitions in all populations. This difference was not a function of coalition size, number of males, socionomic sex ratio, or primiparity, although anecdotal evidence suggests that allomothering may compensate for inept new mothers in related coalitions more often than in unrelated ones. Differences in territory quality could not be ruled out as a potential causal factor in the saturated populations, but were unlikely in the low-density, growing population. There were substantial differences among long-established coalitions in overall reproductive output in all three populations, and this was significantly correlated with the number of breeding females. Increase in coalition size was a function of both group age and the behavioral tolerance among females. Regardless of the underlying reasons for the patterns observed, reproductive success clearly increases with degree of gene correlation among females within cooperative coalitions, and coalitions that recruit more daughters produce more offspring. The nature of the cooperative relationship among group females directly influences both of these outcomes. This is associated with substantial genetic differentiation among social groups within populations, creating conditions in which genetic tendencies towards cooperative behavior can become tightly associated with group reproductive success. Received: 15 September 1999 / Revised: 27 April 2000 / Accepted: 27 May 2000     

Reproduction by subordinates in cooperatively breeding Arabian babblers is uncommon but predictable

In a genetic analysis of the mating system of cooperatively breeding Arabian babblers (Timalidae: Turdoides squamiceps), we identified which individuals in the population are breeding, and how reproductive success was distributed among group members with respect to their dominance rank, for both males and females. The population was characterized by an asymmetrical distribution of reproductive success; behaviorally dominant males produced 176 of 186 (95%) of the offspring in 44 social groups analyzed, and alpha females produced 185 of 186 (99.5%). We evaluated models of reproductive skew by examining genetic and demographic correlates of reproduction by␣subordinates. Subordinate (beta) males that sired young were more likely to be recent dispersers from their natal groups or members of newly formed groups than betas that did not reproduce. Breeding beta males had spent smaller proportions of their lives with the current alpha male and female as alphas than had beta males that did not sire young. One consequence of the linkage of dispersal with breeding in newly formed, nonnatal groups is that beta males that sired young had significantly lower genetic similarity to the alpha males in their groups (based on band-sharing coefficients using multilocus minisatellite DNA fingerprinting) than those that did not sire young. This pattern may occur generally in species in which group membership accrues both through nondispersal of young (forming groups of relatives) as well as through dispersal involving coalitions that sometimes include nonrelatives. Received: 22 July 1997 / Accepted after revision: 5 February 1998     

Brood defense and filial cannibalism in the spottail darter (<Emphasis Type="Italic">Etheostoma squamiceps)</Emphasis>: the effects of parental status and prior experience

Male spottail darters (Etheostoma squamiceps) defend nest sites in which females deposit eggs over the course of several weeks. In laboratory experiments, I tested three predictions of the hypothesis that the presence of eggs increases the value of a nest site to male spottail darters: (1) males should preferentially defend nests with eggs over empty nests, and males that sired the eggs should (2) spend more time defending them and (3) consume less of their broods than should alloparent males. Parent males were tested using eggs they were guarding in the field; alloparents included males that were not defending eggs immediately prior to the experiment (inexperienced), and males that were defending eggs in the field when captured but were given eggs sired by a different male (experienced). In choice experiments in which males were offered nest sites differing only in the presence of eggs, males preferred to defend nest sites with eggs regardless of parental status. Parent males spent significantly more time defending eggs and consumed less of their broods than did inexperienced alloparent males. Experienced alloparent males were similar to parent males in brood defense but had levels of filial cannibalism similar to inexperienced males, suggesting that prior experience may influence brood defense but not egg consumption.