MOLECULAR GENETIC DISSECTION OF SPAWNING,PARENTAGE, AND REPRODUCTIVE TACTICS IN A POPULATION OF REDBREAST SUNFISH,LEPOMIS AURITUS

Despite a great diversity of reproductive behaviors in fishes, few studies have examined the genetic consequences of alternative reproductive tactics. Here we develop and employ microsatellite markers to assess genetic paternity and maternity of progeny cohorts in a population of redbreast sunfish (Lepomis auritus), a species in which males build and tend nests. Nearly 1000 progeny from 25 nests, plus nest-attendant males and nearby adults, were genotyped at microsatellite loci that displayed more than 18 alleles each. The genetic data demonstrate that multiple females (at least two to six) spawned in each nest, their offspring were spatially dispersed across a nest, and more than 90% of the young were sired by the attendant male. However, about 40% of the nests also showed genetic evidence of low-level reproductive parasitism, and two nests were tended by males that had fathered none of the sampled offspring. Genetically deduced reproductive behaviors in this population of redbreast sunfish contrast with those reported previously in bluegill sunfish (L. macrochirus) wherein heteromorphic males specialized for parasitism or for parental care coexist in high frequency. Thus, nest-parasitic reproductive behaviors in fishes appear to be evolutionary labile.     

Intensive genetic assessment of the mating system and reproductive success in a semi-closed population of the mottled sculpin,Cottus bairdi

Most genetic surveys of parentage in nature sample only a small fraction of the breeding population. Here we apply microsatellite markers to deduce the genetic mating system and assess the reproductive success of females and males in an extensively collected, semi-closed stream population of the mottled sculpin fish, Cottus bairdi. In this species, males guard nest rocks where females deposit the eggs for fertilization. The potential exists for both males and females to mate with multiple partners and for males to provide parental care to genetically unrelated offspring. Four hundred and fifty-five adults and subadults, as well as 1,259 offspring from 23 nests, were genotyped at five polymorphic microsatellite loci. Multilocus maternal genotypes, deduced via genetic analyses of embryos, were reconstructed for more than 90% of the analysed nests, thus allowing both male and female reproductive success to be estimated accurately. There was no genetic evidence for cuckoldry, but one nest probably represents a takeover event. Successful males spawned with a mean of 2.8 partners, whereas each female apparently deposited her entire clutch of eggs in a single nest (mean fecundity = 66 eggs/female). On average, genetically deduced sires and dams were captured 1.6 and 9.3 metres from their respective nests, indicating little movement by breeders during the spawning season. Based on a 'genetic mark-recapture' estimate, the total number of potentially breeding adults (c. 570) was an order-of-magnitude larger than genetically based estimates of the effective number of breeders (c. 54). In addition, significantly fewer eggs per female were deposited in single than in multidam nests. Not only were perceived high-quality males spawning with multiple partners, but they were receiving more eggs from each female.     

The Mating System of Steelhead, Oncorhynchus mykiss, Inferred by Molecular Analysis of Parents and Progeny

The development of molecular markers has allowed behavioral ecologists to link parents to specific offspring, providing insights into breeding systems that were not apparent from direct observations of the social system. Studies of this type in fishes have focused on species with male parental care such as centrarchids, and on salmonids, a family with little parental care. In order to gain further insight into the mating system of steelhead trout, Oncorhynchus mykiss, a winter-spawning species whose reproductive system is poorly known, adults returning to spawn were captured in four consecutive years in a small, unfished, wild population. Juvenile offspring were sampled by electrofishing and parentage was determined by exclusion based on a 12 locus microsatellite genotype. Both males and females mated with multiple individuals, though single pair matings were also inferred. Females and males tended to have the same number of mates (median = 1), but males were more likely to have no apparent partner (43% vs. 23% for females) and the maximum number of mates were obtained by males (range 0–10 vs. 0–5 for females). There was no difference in median arrival date by sex, but 80% of the females mated with males that had already arrived rather than males arriving with or after the females (median = 7.5, range = 1–63 days difference). Contrary to expectations, there was no evidence of size-assortative mating; larger males and larger females did not tend to mate with each other more often than would have occurred by chance. Of the juveniles with only one identified parent, most had a known mother and an unknown father rather than the reverse (88% vs. 11%). We interpret this as indirect evidence that non-anadromous males achieved a significant number of fertilizations. Thus the steelhead mating system was complex, being more strongly structured by arrival date than fish size, and including a significant genetic contribution by mature male parr.     

Patterns of multiple paternity and maternity in fishes

The characterization of patterns of multiple mating is a major facet of molecular ecology and is paramount to understanding the evolution of behaviours associated with parental care and mate choice. Over the last 15 years, fishes have been particularly well studied with respect to multiple maternity and paternity thanks to the widespread application of microsatellite markers. The present review focusses on the impressive literature on genetic parentage in fishes. In studies of natural populations, we find that multiple paternity is extremely common across fish species, whereas rates of multiple maternity are much more variable. In species with nest defence, for example, rates of multiple maternity are strongly bimodal, and the occurrence of multiple dams per brood is either rare or the rule. The sex of the care‐giving parent is correlated with the rate of multiple parentage: when males provide uniparental care, rates of multiple paternity are low compared to rates of multiple maternity; when females provide parental care, either alone or assisted by males, rates of multiple paternity are highly variable, whereas rates of multiple maternity are quite low. These patterns may reflect conflicts between the reproductive interests of males and females. We also find that fishes in which females brood the offspring internally display much higher rates of multiple paternity compared to mammals or birds, whereas reptiles are intermediate. Male‐nesting fish species, however, show rates of multiple paternity more similar to those found in other vertebrates. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 735–760.     

The evolution of parental care

Our understanding of parental care behavior can be significantly advanced through the application of Williams's Principle, which states that reproduction has not only a benefit but also a cost to lifetime fitness. My laboratory has formalized Williams's Principle into the relative value theorem and found that its application to fishes, the taxa with the most diverse patterns of parental care, can help to explain which sex provides care and how much. In fishes, it is often the male that provides parental care, not because the male obtains greater benefits from this care, but probably because he pays fewer costs. Fish dynamically adjust their investment into parental care according to the number of offspring in their brood, past investment, genetic relatedness, and alternative mating opportunities, all of which affect the value of current offspring relative to potential future offspring. These results may also help us understand the joy and the challenges of parental care in humans.     

Mating systems and sexual selection in male-pregnant pipefishes and seahorses: insights from microsatellite-based studies of maternity

In pipefishes and seahorses (family Syngnathidae), the males provide all postzygotic care of offspring by brooding embryos on their ventral surfaces. In some species, this phenomenon of male "pregnancy" results in a reversal of the usual direction of sexual selection, such that females compete more than males for access to mates, and secondary sexual characteristics evolve in females. Thus the syngnathids can provide critical tests of theories related to the evolution of sex differences and sexual selection. Microsatellite-based studies of the genetic mating systems of several species of pipefishes and seahorses have provided insights into important aspects of the natural history and evolution of these fishes. First, males of species with completely enclosed pouches have complete confidence of paternity, as might be predicted from parental investment theory for species in which males invest so heavily in offspring. Second, a wide range of genetic mating systems have been documented in nature, including genetic monogamy in a seahorse, polygynandry in two species of pipefish, and polyandry in a third pipefish species. The genetic mating systems appear to be causally related to the intensity of sexual selection, with secondary sex characters evolving most often in females of the more polyandrous species. Third, genetic studies of captive-breeding pipefish suggest that the sexual selection gradient (or Bateman gradient) may be a substantially better method for characterizing the mating system than previously available techniques. Finally, these genetic studies of syngnathid mating systems have led to some general insights into the occurrence of clustered mutations at microsatellite loci, the utility of linked loci in studies of parentage, and the use of parentage data for direct estimation of adult population size.     

Diverse parentage relationships in paternal mouthbrooding fishes

While mouthbrooding is not an uncommon parental care strategy in fishes, paternal mouthbrooding only occurs in eight fish families and is little studied. The high cost of paternal mouthbrooding to the male implies a low risk of investment in another male''s offspring but genetic parentage patterns are poorly known for paternal mouthbrooders. Here, we used single-nucleotide polymorphism genetic data to investigate parentage relationships of broods of two mouthbrooders of northern Australian rivers, mouth almighty Glossamia aprion and blue catfish Neoarius graeffei. For N. graeffei, we found that the parentage pattern was largely monogamous with the brooder male as the sire. For G. aprion, the parentage pattern was more heterogeneous including observations of monogamous broods with the brooder male as the sire (73%), polygyny (13%), cuckoldry (6%) and a brood genetically unrelated to the brooder male (6%). Findings demonstrate the potential for complex interrelationships of male care, paternity confidence and mating behaviour in mouthbrooding fishes.     

Does Social Mating System Influence Nest Defence Behaviour in Great Reed Warbler (Acrocephalus arundinaceus) Males?

In birds with biparental care, males and females often conflict over how much care to provide to their offspring and it may be substantially influenced by increased level of polygamy. In accordance with sexual conflict theory, males of socially polygynous bird species provide much less care to their nestlings than do males of most socially monogamous species. Most of previous studies, however, have used feeding behaviour as an index for variations in male parental care only. However, this may be skewed if polygynous males compensate for lower feeding assistance through the provision of other parental care such as protection of nests from predators. In this paper, we examine nest defence behaviour in the facultatively polygynous great reed warbler with respect to sex and type of social mating system. We recorded latency to the first arrival, distance from the predator and defensive reaction of each parent towards a human intruder. Socially polygynous males with two simultaneously active nests defended primary females’ nests less vigorously than socially monogamous males, whereas no differences were found between monogamous and primary females. Generally, however, they took a bigger role in nest defence than males in all cases. Our results support an idea that sexual conflict is driven by polygamy and that type of social mating system can influence nest defence behaviour of facultatively polygynous birds. This finding should be taken into consideration when studying nest defence parental care in polygynous mating systems.     

Female Mate Choice in a Paternal Brooding Blenny: The Process and Benefits of Mating with Males Tending Young Eggs

Female mate preference for males tending young offspring has been demonstrated in many fishes; however, not much is known about the choice process. Using the barred chin blenny Rhabdoblennius ellipes, a fish with male uniparental care, field experiments were conducted to investigate the female preference for males tending young eggs and then whether females choose the males with young eggs by discriminating young eggs from old eggs in the nests. Males tending young eggs (0‐ to 2‐d old) acquired new eggs nine times more frequently than those tending old eggs (3‐ to 5‐d old) regardless of other traits in males and nests. In the two egg‐switching field experiments (old to young and young to old), contrary to our expectation, male mating success was neither enhanced when given young eggs nor inhibited when given old eggs. These results suggested that females choose males with young eggs not by discriminating the developmental stage of eggs in the nests but by using other choice processes. By choosing males with young eggs, females may benefit from the dilution effects of egg predation and filial cannibalism risks and avoid male parental care failure.     

Animal breeding systems

The study of breeding systems explores relationships between mating behaviour and parental care. Recent findings have shown that in many birds, fishes, anurans, and insects, females play a more active role than previously thought, by engaging in mate choice, mating with more than one male, and selecting genetic partners separately from social partners. Theoretical advances have improved our understanding of the effect of parental care on sex differences in mating behaviour, though less attention has been devoted to feedback in the opposite direction. The original emphasis on the role of ecology in determining breeding systems has been overshadowed by studies of individual interactions, but modern comparative techniques may provide a new fusion between ecology, life histories, and reproductive behaviour.     

A model for evolution of male parental care and female multiple mating

In most animals, males gain a fitness benefit by mating with many females, whereas the number of progeny per female is unlikely to increase as a function of additional mates. Furthermore, males of internally fertilizing species run the risk of investing in offspring of other males if they provide parental care. Nevertheless, males of many avian species and a minority of mammalian species provide parental care, and females of various species mate with multiple males. I investigate a two-locus genetic model for evolution of male parental care and female multiple mating in which females gain a direct benefit by multiple mating from the paternal care they thereby elicit for their offspring. The model suggests that, first, male parental care can evolve when it strongly enhances offspring survival and the direct costs of female multiple mating (e.g., loss of energy, risk of injury, exposure to infectious diseases) are greater than its indirect benefit (e.g., acquisition of good genes, increased genetic diversity among offspring); second, female multiple mating can evolve when paternal care is important for offspring survival or the indirect benefit of multiple mating is larger than its direct cost; and, finally, male parental care and female multiple mating can co-occur.     

The unexpected but understandable dynamics of mating,paternity and paternal care in the ocellated wrasse

Although theory generally predicts that males should reduce paternal care in response to cues that predict increased sperm competition and decreased paternity, empirical patterns are equivocal. Some studies have found the predicted decrease in male care with increased sperm competition, while even more studies report no effect of paternity or sperm competition on male care. Here, we report the first example, to our knowledge, of paternal care increasing with the risk and intensity of sperm competition, in the ocellated wrasse (Symphodus ocellatus). Theory also predicts that if paternal care varies and is important to female fitness, female choice among males and male indicators traits of expected paternal care should evolve. Despite a non-random distribution of mating success among nests, we found no evidence for female choice among parental males. Finally, we document the highest published levels of extra-pair paternity for a species with exclusive and obligate male care: genetic paternity analyses revealed cuckoldry at 100 per cent of nests and 28 per cent of all offspring were not sired by the male caring for them. While not predicted by any existing theory, these unexpected reproductive patterns become understandable if we consider how male and female mating and parental care interact simultaneously in this and probably many other species.     

High rates of extra‐pair paternity in a socially monogamous beetle with biparental care

1. Nest construction and paternity assurance are predicted to favour biparental care in insects. The horned passalus (Odontotaenius disjunctus) is a socially monogamous beetle with biparental care that breeds in decaying logs. The genetic mating system of the horned passalus was investigated to determine if paternity assurance is likely to drive the evolution or maintenance of paternal care in this system. Parental time budgets were also examined to better understand the types and frequencies of behaviours performed by parents. 2. Genotyping‐by‐sequencing revealed high levels of extra‐pair paternity, with 54.8% of offspring sired by extra‐pair males and 70% of nests containing extra‐pair young. 3. More heterozygous social males were cuckolded less than more homozygous social males. Extra‐pair mating, however, seems unlikely to increase offspring genetic diversity as extra‐pair offspring were not more heterozygous than within‐pair offspring, and average brood heterozygosity did not increase with higher rates of extra‐pair paternity. 4. Behavioural observations demonstrated that parents spent on average 46.5% of their time processing the decaying wood resource for larval offspring. Because resource processing is a by‐product of feeding and provides shareable benefits for all larvae in the brood, this form of paternal care could be favoured despite low paternity.     

Genetic paternity analysis and breeding success in bluegill sunfish (Lepomis macrochirus)

Fish have some of the most complex mating systems known in the animal kingdom. With the advent of powerful genetic markers and an emerging mathematical framework to calculate parentage, it is now possible to analyze genetic relatedness and gene flow in these systems. An important example is the bluegill sunfish (Lepomis macrochirus) which consists of parental males that provide sole care for the young, cuckolder males that parasitize the parentals, and females that actively choose among males within dense breeding colonies. In this article genetic markers for bluegill are characterized and their utility in parentage studies is demonstrated by calculating the genetic relatedness of parental males to their broods for an entire natural breeding colony. A novel Monte Carlo simulation is developed to calculate the confidence in the relatedness estimates and these data are used to provide an estimate of the mean breeding success of parental and cuckolder males. Finally, the applications of genetic analyses to understanding mating systems, parental care, and life-history evolution in bluegill are discussed.     

Don'T put all your eggs in one nest: spread them and cut time at risk

Abstract In many egg-laying animals, some females spread their clutch among several nests. The fitness effects of this reproductive tactic are obscure. Using mathematical modeling and field observations, we analyze an unexplored benefit of egg spreading in brood parasitic and other breeding systems: reduced time at risk for offspring. If a clutch takes many days to lay until incubation and embryo development starts after the last egg, by spreading her eggs a parasitic female can reduce offspring time in the vulnerable nest at risk of predation or other destruction. The model suggests that she can achieve much of this benefit by spreading her eggs among a few nests, even if her total clutch is large. Field data from goldeneye ducks Bucephala clangula show that egg spreading enables a fecund female to lay a clutch that is much larger than average without increasing offspring time at risk in a nest. This advantage increases with female condition (fecundity) and can markedly raise female reproductive success. These results help explain the puzzle of nesting parasites in some precocial birds, which lay eggs in the nests of other females before laying eggs in their own nest. Risk reduction by egg spreading may also play a role in the evolution of other breeding systems and taxa-for instance, polyandry with male parental care in some birds and fishes.     

Alloparental care in the sea: Brood parasitism and adoption within and between two species of coral reef Altrichthys damselfish?

The evolution of parental care opens the door for the evolution of brood parasitic strategies that allow individuals to gain the benefits of parental care without paying the costs. Here we provide the first documentation for alloparental care in coral reef fish and we discuss why these patterns may reflect conspecific and interspecific brood parasitism. Species‐specific barcodes revealed the existence of low levels (3.5% of all offspring) of mixed interspecific broods, mostly juvenile Amblyglyphidodon batunai and Pomacentrus smithi damselfish in Altrichthys broods. A separate analysis of conspecific parentage based on microsatellite markers revealed that mixed parentage broods are common in both species, and the genetic patterns are consistent with two different modes of conspecific brood parasitism, although further studies are required to determine the specific mechanisms responsible for these mixed parentage broods. While many broods had offspring from multiple parasites, in many cases a given brood contained only a single foreign offspring, perhaps a consequence of the movement of lone juveniles between nests. In other cases, broods contained large numbers of putative parasitic offspring from the same parents and we propose that these are more likely to be cases where parasitic adults laid a large number of eggs in the host nest than the result of movements of large numbers of offspring from a single brood after hatching. The evidence that these genetic patterns reflect adaptive brood parasitism, as well as possible costs and benefits of parasitism to hosts and parasites, are discussed.     

Sexual selection determines parental care patterns in cichlid fishes

Despite a massive research effort, our understanding of why, in most vertebrates, males compete for mates and females care for offspring remains incomplete. Two alternative hypotheses have been proposed to explain the direction of causality between parental care and sexual selection. Traditionally, sexual selection has been explained as a consequence of relative parental investment, where the sex investing less will compete for the sex investing more. However, a more recent model suggests that parental care patterns result from sexual selection acting on one sex favoring mating competition and lower parental investment. Using species-level comparative analyses on Tanganyikan cichlid fishes we tested these alternative hypotheses employing a proxy of sexual selection based on mating system, sexual dichromatism, and dimorphism data. First, while controlling for female reproductive investment, we found that species with intense sexual selection were associated with female-only care whereas species with moderate sexual selection were associated with biparental care. Second, using contingency analyses, we found that, contrary to the traditional view, evolutionary changes in parental care type are dependent on the intensity of sexual selection. Hence, our results support the hypothesis that sexual selection determines parental care patterns in Tanganyikan cichlid fishes.     

Do Male Desert Gobies Compromise Offspring Care to Attract Additional Mating Opportunities?

Males often play a critical role in offspring care but the time and energy invested in looking after young can potentially limit their ability to seek out additional mating opportunities. Recent studies, however, suggest that a conflict between male parental effort and mating effort may not always be inevitable, especially if breeding occurs near the nest, or if parental behaviours are under sexual selection. Accordingly, we set out to experimentally investigate male care and courtship in the desert goby Chlamydogobius eremius, a nest-guarding fish with exclusive paternal care. Despite courtship occurring near the nest, we found that when egg-tending males were given the opportunity to attract additional females, they fanned their eggs less often, engaged in shorter fanning bouts, and spent more of their time outside their nests courting. Our findings highlight the importance of understanding the circumstances under which reproductive tradeoffs are expected to occur and how these, in turn, operate to influence male reproductive decisions.     

Evolutionary pathways in shorebird breeding systems: sexual conflict, parental care, and chick development

Sexual selection, mating opportunities, and parental behavior are interrelated, although the specific nature of these relationships is controversial. Two major hypotheses have been suggested. The parental investment hypothesis states that the relative parental investment of the sexes drives the operation of sexual selection. Thus, the sex that invests less in offspring care competes more intensely and monopolizes access to mates. The sexual conflict hypothesis proposes that sexual selection (the competition among both males and females for mates), mating opportunities, and parental behavior are interrelated and predicts a feedback loop between mating systems and parental care. Here we test both hypotheses using a comprehensive dataset of shorebirds, a maximum-likelihood statistical technique, and a recent supertree of extant shorebirds and allies. Shorebirds are an excellent group for these analyses because they display unique variation in parental care and social mating system. First, we show that chick development constrains the evolution of both parental care and mate competition, because transitions toward more precocial offspring preceded transitions toward reduced parental care and social polygamy. Second, changes in care and mating systems respond to one another, most likely because both influenced and are influenced by mating opportunities. Taken together, our results are more consistent with the sexual conflict hypothesis than the parental investment hypothesis.     

The genetic mating system of spotted sunfish (Lepomis punctatus): mate numbers and the influence of male reproductive parasites

In nest-building fish species, mature males often exhibit one of two alternative reproductive behaviours. Bourgeois males build nests, court females, and guard their eggs. Parasitic cuckolders attempt to steal fertilizations from bourgeois males and do not invest in parental care. Previous evidence from the bluegill sunfish (Lepomis macrochirus) suggests that adult males are morphologically specialized for these two tactics. Here, we used microsatellite markers to determine genetic parentage in a natural population of the spotted sunfish (L. punctatus) that also displayed both bourgeois and parasitic male morphs. As gauged by relative investments in gonadal vs. somatic tissues, between 5 and 15% of the mature adult males were parasites. Multi-locus genotypes were generated for more than 1400 embryos in 30 nests, their nest-guardian males, and for other adults in the population. Progeny in approximately 57% of the nests were sired exclusively by the guardian male, but the remaining nests contained embryos resulting from cuckoldry as well. Overall, the frequency of offspring resulting from stolen fertilizations was only 1.3%, indicating that the great majority of paternity is by bourgeois nesting males. With regard to maternity, 87% of the nests had at least three dams, and computer simulations estimate that about 7.2 dams spawned per nest.