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.     

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.     

Major benefits of guarding behavior in subsocial bees: implications for social evolution

Parental care is a behavior that increases the growth and survival of offspring, often at a cost to the parents' own survival and/or future reproduction. In this study, we focused on nest guarding, which is one of the most important types of extended parental care; we studied this behavior in two solitary bee species of the genus Ceratina with social ancestors. We performed the experiment of removing the laying female, who usually guards the nest after completing its provisioning, to test the effects of nest guarding on the offspring survival and nest fate. By dissecting natural nests, we found that Ceratina cucurbitina females always guarded their offspring until the offspring reached adulthood. In addition, the females of this species were able to crawl across the nest partitions and inspect the offspring in the brood cells. In contrast, several Ceratina chalybea females guarded their nests until the offspring reached adulthood, but others closed the nest entrance with a plug and deserted the nest. Nests with a low number of provisioned cells were more likely to be plugged and abandoned than nests with a higher number of cells. The female removal experiment had a significantly negative effect on offspring survival in both species. These nests frequently failed due to the attacks of natural enemies (e.g., ants, chalcidoid wasps, and other competing Ceratina bees). Increased offspring survival is the most important benefit of the guarding strategy. The abandonment of a potentially unsuccessful brood might constitute a benefit of the nest plugging behavior. The facultative nest desertion strategy is a derived behavior in the studied bees and constitutes an example of an evolutionary reduction in the extent of parental care.     

Biotic and abiotic factors affecting survival of early life history intervals of a stream-dwelling sunfish

Synopsis Biotic interactions, such as competition and predation, and abiotic events, such as floods, both have important consequences for organisms inhabiting warmwater streams. Empirical studies can lead to better understanding of how these factors interact to affect distinct life history intervals of stream fishes. Survival of eggs, embryos and larvae in nests of longear sunfishLepomis megalotis was monitored in a section of Jordan Creek for four years. During two years characterized by low, relatively stable flow, nest failures could be attributed to biotic interactions. During two years with more variable flow, most brood losses occurred during floods. Flooding led to nest desertion and loss of offspring regardless of nest location. The number of nests constructed tended to be lower during years with more variable flow. The proportion of nests with successful broods did not differ between colonial and solitary nests. Variation in flow regime modifies the importance of biotic effects on survival of early life history intervals of longear sunfish.     

Sources of variation in the nesting success of understory tropical birds

Survival of offspring is a key fitness component and, for birds, the threat of predation on nests is especially influential. Data on rates of nest success from tropical regions are comparatively few, conservation‐relevant, and essential for assessing the validity of models comparing the life histories and behavior or birds across latitudinal gradients. We monitored over 2 000 nests in the lowland forests of central Panama and, using the logistic exposure to model the fate of nests, explored the importance of variation in rate of nest success according to type of nest, height of nests, among years, in early versus late nests, and at different stages of the nest cycle. Analyses of over 1 400 nests for 18 species revealed considerable variation among species in the daily survival rate of nests (range among 18 species=0.91 to 0.98), but nest type and stage of the nesting cycle were generally influential on the probability of nest success. Cavity or enclosed nesters experienced greater nest success than open cup nesters and rates of nest loss were generally greatest in the nestling stage. We found limited evidence that height of nests affected probability of success, but no indication that timing of nesting effort was influential. Despite the occurrence of a severe ENSO event during our sampling, annual variation in nest success was not consistent among species. Interspecific variation in the rates and patterns of nest predation in our study, coupled with reports of high rates of nest loss at temperate latitudes, lead us to question long standing assumptions about latitudinal trends in rates of nest loss. We urge further work to understand the implications of nest predation on the evolutionary ecology of tropical birds.     

The importance of microclimate variation in determining size,growth and survival of avian offspring: experimental evidence from a cavity nesting passerine

Organisms are expected to balance energy allocation in such a way that fitness is maximized. While much research has focussed on allocation strategies of reproducing parents, in particular birds, relatively little attention has been paid to how nestlings allocate energy while in the nest. Nestling birds are faced with a trade-off between devoting energy to growth or to thermoregulation, and in altricial species it is likely that the thermal environment of the nest site influences the nature of this trade-off. Here, we experimentally investigate how altering the microclimate of nests affects the growth, size and survival, as well as cell-mediated immune (CMI) response, of nestling tree swallows (Tachycineta bicolor) in a temperate environment. We place air-activated heating pads in nests of swallows when young were between 4 days and 16 days of age, and compared performance of offspring to control nests. Our manipulation raised temperatures of heated nests by approximately 5°C compared to control nests. Offspring in heated nests had enhanced survival while in the nest, and we also found that they were heavier and had longer ninth primary feathers at 16 days of age. In addition, heating nest boxes resulted in significantly faster growth of primaries, and there was a trend for growth rates of mass to also be higher in heated nests. There were no significant differences between heated and control nests in growth rate or size of tarsus at age 16 days, and we speculate that this lack of response to elevated nest temperatures may be due to growth of skeletal structures being limited by other factors such as calcium availability. We also found no difference between heated and control nests in CMI response. Nonetheless, our results show overall that increasing temperatures of nests has significant benefits that enhance the fitness of offspring. As provisioning rates to offspring did not differ between heated and control nests, we suspect that the beneficial effects of heating were not the consequence of changes in parental behaviour. Our results provide insight into factors, other than food supply, that have important consequences in determining reproductive success of birds breeding in temperate environments.     

Effects of the Nest Web and Female Attendance on Survival of Young in the Subsocial Spider Mite Schizotetranychus Longus (Acari: Tetranychidae)

The subsocial spider mite Schizotetranychus longus lives gregariously in woven nests on leaves of Sasa bamboo. Adults of both sexes defend their young against the predatory mite Typhlodromus bambusae. The effects of web and female attendance of this species on offspring survival were evaluated in a natural forest. Experimental removal of web and females revealed that S. longus young suffered greater mortality than in the control. Furthermore, the web made by parent females had a positive effect on offspring survival, possibly through preventing predators from intruding into the nest. Attendance of a female in a nest also had an effect on improving the survival rate of her offspring over a short period. We could not detect any function of the web and female other than protection against predators at least for the 5 day period of the experiment. The nest web of S. longus has an important function in the survival of young by preventing the entry of pedestrian predators (generalist) and females may play a role in defending against specialized predators which can intrude into the nests.     

Effect of prey quantity and temperature on nest demography of social wasps

Abstract. 1. To determine the effect of prey quantity and temperature on nest demography of social wasps ( Polistes fuscatus ), field experiments were conducted, in which wasps were provided with a low quantity of caterpillars (approximately nest subsistence level) or high quantity (three times as much). In addition, in the third year, the nest boxes were modified to be relatively cool (white and insulated) or warm (black).
2. In 1997 and 1998, high-food nests had a high proportion of cells containing developing offspring, produced more offspring, and had disproportionately more female offspring compared with low-food nests.
3. In 1999, the cool and warm nest boxes exhibited a daily average difference of 1.3 °C and a maximum difference of 6.9 °C. The warm high-food nests produced more offspring than any other treatment. The cool high-food nests produced similar numbers of offspring as the cool low-food and warm low-food treatments.
4. As indicated by a surplus of uncapped cells, foundresses of low-food nests, which would have had the egg-laying potential to produce many offspring, apparently sacrificed eggs to provide a food supplement for the developing offspring. This pattern plus more time observed foraging suggests considerable expenditure of energy by foundresses, in response to the low supply of food.
5. Importantly, these results indicate that an interactive effect of prey quantity and temperature on offspring production occurred, which may reflect the different effects on developmental rate and growth rate at cool versus warm nest temperatures.     

The effect of wind on the rate of heat loss from avian cup-shaped nests

Forced convection can significantly influence the heat loss from birds and their offspring but effects may be reduced by using sheltered micro-sites such as cavities or constructing nests. The structural and thermal properties of the nests of two species, the spiny-cheeked honeyeater (Acanthagenys rufogularis) and yellow-throated miner (Manorina flavigula), were measured in relation to three wind speeds. Nest dimensions differ between the two species, despite the similar body mass of the incubating adults, however nest conductance is comparable. As wind speed increases, so does the rate of heat loss from the nests of both species, and further still during incubation recesses. The significance of forced convection through the nest is a near-doubling in heat production required by the parent, even when incubating at relatively low wind speeds. This provides confirmation that selecting a sheltered nest site is important for avian reproductive success.     

Increased performance of offspring sired by parasitic males in bluegill sunfish

Males of many species are characterized by alternative matingtactics. In bluegill sunfish (Lepomis macrochirus), some malesdelay maturation and become "parentals" while other males matureprecociously and become "cuckolders." Parentals use an overt,territorial mating tactic, defending a nest and courting females.Cuckolders instead use a sneaking tactic to parasitize parentals.It has previously been shown that parentals that are heavilycuckolded provide less care to their young, yet females do notappear to discriminate against cuckolders, and they may actuallyrelease more eggs when a cuckolder is present than when spawningonly with a parental. Here I examined growth rate of fry ofknown paternity through the yolk-sac stage of development usingcomplementary laboratory and field studies to assess a potentialindirect benefit for females that mate with cuckolders. Comparisonof maternal half-siblings sired in vitro shows that cuckolderoffspring grow faster and to a larger size than parental offspringwhile feeding endogenously on their yolk sac. Because both foodresource and maternal genes are equivalent across treatments,these data indicate a genetic difference in growth between thetwo male life histories. In the field, fry from nests that haveproportionately more cuckolder offspring are larger when theyemerge from the nest. This increased size can lead to threefoldhigher survivorship for cuckolder offspring than parental offspringfrom Hydra canadensis predation, a major predator of bluegillfry. These results are discussed in the context of mate choicefor direct and indirect benefits and in the context of the evolutionof alternative mating tactics.     

Maternal investment in a bee species with facultative nest guarding and males heavier than females

1. Maternal investment can be influenced by several factors, especially maternal quality and possibilities for future reproduction. Mass provisioning Hymenoptera are an excellent group for measuring maternal investment because mothers distribute food sources to each brood cell for each offspring separately. Generally in aculeate Hymenoptera, larger females produce larger offspring and invest more in female offspring than in male offspring. 2. This study investigated patterns of maternal investment in Ceratina chalcites, which has an uncommon type of sexual size dimorphism in Hymenoptera: on average, males are heavier than females. It was found that larger females produce a significantly higher proportion of male offspring, as males are the costlier sex in this species. 3. Facultative nest guarding by females was observed. Females can guard offspring until adulthood, as is typical for bees of genus Ceratina (34.43% of nests); however, in the majority of cases (65.56% of nests), females plug and abandon the nest. Significant differences were found in the amount of investment between guarded and unguarded nests. Guarded nests had a greater number of provisioned brood cells and a higher proportion of male offspring. It is suggested that mothers have two facultative strategies – either she makes a large investment in the offspring of one nest or she abandons the first nest and carries out a second nesting elsewhere.     

Females compensate for moult‐associated male nest desertion in Hooded Warblers

Uniparental offspring desertion occurs in a wide variety of avian taxa and usually reflects sexual conflict over parental care. In many species, desertion yields immediate reproductive benefits for deserters if they can re‐mate and breed again during the same nesting season; in such cases desertion may be selectively advantageous even if it significantly reduces the fitness of the current brood. However, in many other species, parents desert late‐season offspring when opportunities to re‐nest are absent. In these cases, any reproductive benefits of desertion are delayed, and desertion is unlikely to be advantageous unless the deserted parent can compensate for the loss of its partner and minimize costs to the current brood. We tested this parental compensation hypothesis in Hooded Warblers Setophaga citrina, a species in which males regularly desert late‐season nestlings and fledglings during moult. Females from deserted nests effectively doubled their provisioning efforts, and nestlings from deserted nests received just as much food, gained mass at the same rate, and were no more likely to die from either complete nest predation or brood reduction as young from biparental nests. The female provisioning response, however, was significantly related to nestling age; females undercompensated for male desertion when the nestlings were young, but overcompensated as nestlings approached fledging age, probably because of time constraints that brooding imposed on females with young nestlings. Overall, our results indicate that female Hooded Warblers completely compensate for male moult‐associated nest desertion, and that deserting males pay no reproductive cost for desertion, at least up to the point of fledging. Along with other studies, our findings support the general conclusion that late‐season offspring desertion is likely to evolve only when parental compensation by the deserted partner can minimize costs to the current brood.     

Thermal and fitness-related consequences of nest location in Painted Turtles (Chrysemys picta)

1. Laboratory experiments have documented substantial temperature effects on the physiological ecology of reptilian eggs, embryos and offspring. However, functional links between important habitat characteristics, nest microenvironments and fitness-related traits of neonates in natural nests have rarely been studied.
2. A field study of 11 Painted Turtle ( Chrysemys picta ) nests was conducted to quantify the relationships between a habitat characteristic (i.e. vegetational cover around nests at oviposition) and (1) developmental temperature and its effect on offspring sex ratio and (2) hibernation temperature and its effect on offspring survivorship.
3. Vegetational cover was negatively correlated with nest temperatures in July, the period when offspring sex is determined. However, neither vegetational cover nor mean nest temperature predicted nest sex ratios, although correlations among these variables were consistent with causal relationships derived from laboratory studies.
4. Summer vegetational cover was also negatively correlated with measures of winter nest temperatures. Of the three nests exhibiting overwinter mortality, two were surrounded by thick vegetation and all experienced temperatures below – 8 °C. The remaining nests reached temperatures as low as – 6 °C without mortality, indicating that hatchlings in these nests exhibited remarkable supercooling ability.
5. The results suggest that habitat characteristics and nest microenvironments are functionally linked and have fitness consequences for both embryos and offspring, implying that nest-site choice by female turtles could have considerable utility.     

Colony success of the submissive ant Formica fusca within territories of the dominant Formica polyctena

Abstract. 1. Twenty-three nests of the submissive ant Formica fusca L. were sampled in two adjacent territories of the dominant wood ant Formica polyctena Först. The nests were dug up at different distances from the wood-ant mounds. Distance is assumed to be inversely related to the extent of disturbance of F. fusca by F. polyctena.
2. Colony success of F. fusca was assayed by counting the numbers of workers (colony size), and worker and sexual offspring in a nest. For individual size, the head width and dry weight of fifty workers per nest were measured.
3. Colony size correlated positively with the numbers of worker and sexual offspring in one territory, but only with worker offspring in the other.
4. Distance from the wood-ant mound correlated positively with colony size and numbers of worker and female offspring in one territory. In the other territory distance correlated positively with number of females, but negatively with number of worker offspring. No significant correlations between distance and the size measurements were obtained.
5. Because of its nonaggressive behaviour F. fusca may nest fairly close to a wood-ant mound but is likely to show reduced abundances in terms of nest density and forager number, and, ultimately, lowered fitness.     

Extreme sequential polyandry insures against nest failure in a frog

Sequential polyandry may evolve as an insurance mechanism to reduce the risk of choosing a mate that is infertile, closely related, genetically inferior or incompatible, but polyandry also might insure against nest failure in unpredictable environments. Most animals are oviparous, and in species where males provide nest sites whose quality varies substantially and unpredictably, polyandrous females might insure offspring success by distributing their eggs across multiple nests. Here, we test this hypothesis in a wild population of an Australian terrestrial toadlet, a polyandrous species, where males construct nests and remain with broods. We found that females partitioned their eggs across the nests of two to eight males and that more polyandrous females gained a significant increase in mean offspring survivorship. Our results provide evidence for the most extreme case of sequential polyandry yet discovered in a vertebrate and also suggest that insurance against nest failure might favour the evolution of polyandry. We propose that insurance against nest failure might be widespread among oviparous taxa and provide an important explanation for the prevalence of sequential polyandry in nature.     

The discovery of hatching and transition to feeding young by male Mountain Bluebirds

In many bird species, only females incubate the eggs, but both sexes feed nestlings. The means by which males of such species discover hatching and transition to feeding their offspring remains almost completely unexplored. Of particular interest are species with nests whose contents are concealed from view. During June and early July 2015 in the Bighorn Mountains of Wyoming, we used continuous video‐recording of nests of cavity‐nesting Mountain Bluebirds (Sialia currucoides) to document the transition to feeding young by males. We saw no evidence that females used distinct vocal or visual displays to signal hatching to males. Observing mates carrying eggshells away from, or food into, nest boxes did not appear to trigger provisioning by males. Rather, at all 24 nests observed, males did not begin feeding until they had come to nest boxes and presumably sensed the presence of hatchings directly. Individual males varied, however, in both the manner in which they inspected nest contents and the number of times they did so before starting to feed young. Although most males fully entered nest boxes where they could see, touch, hear, and possibly smell hatchlings (or eggshell parts), other males may have detected hatchlings only by sound or possibly smell while perched at a nest‐box entrance. Based on past studies of mice and doves, we suggest that, for provisioning behavior to begin, some kind of direct sensation of offspring may be necessary to activate relevant neurons in the medial preoptic area of the hypothalamus of males, an area of the brain important in parental care. Additional research is necessary to test this, and to examine the effects of factors such as hormone levels and breeding experience on the means and rapidity by which males discover hatching and transition to nestling provisioning.     

Genetic perspectives on the natural history of fish mating systems

Molecular analyses of bird and mammal populations have shown that social mating systems must be distinguished from genetic mating systems. This distinction is important in fishes also, where the potential for extrapair spawning and intraspecific brood parasitism is especially great. We review studies on fishes that have used molecular markers to document biological parentage and genetic mating systems in nature, particularly in species with extended parental care of offspring. On average, nest-guarding adults parented about 70-95% of their custodial offspring, and approximately one-third of the nests were cuckolded to some extent. Furthermore, nearly 10% of the assayed nests contained offspring tended by foster fathers either because of nest takeovers or egg thievery. On average, fish that provide parental care on nests spawned with more mates than did fish with internal fertilization and pregnancy. Overall, genetic markers have both confirmed and quantified the incidence of several reproductive and other social behaviors of fishes, and have thereby enhanced our knowledge of piscine natural history.     

Birds adopting weaver nests for breeding in Africa

Weavers build domed, long-lasting nests that may also be adopted by other species for breeding, probably reducing the energetic costs of nest building to varying degrees. In an extensive literature search, 57 species were found to have at least one record of adopting a weaver nest. There is one known obligate nest user, the Pygmy Falcon Polihierax semitorquatus. Four species were classed as near obligate nest adopters. Four species were listed as common, 10 as occasional, and 38 species as rare nest adopters. Other than the falcon and lovebirds Agapornis species, these nest adopters are passerines. Of the 57 species of nest adopters, 35 species had confirmed eggs and/or chicks found in the weaver nests. Most nest adopter species were in the Estrildidae family (20 species), with three estrildids classed as near obligates. This was followed by the Muscicapidae family, species that build cup nests. By building their cup nests inside weaver nests, there is likely protection from adverse weather and predators. Overall, there appeared to be a large diversity of nest adopter species for the traditional savanna living weavers (Ploceus, Bubalornis, Anaplectes, Plocepasser and Philetairus).     

Nest‐site selection by crocodiles at a rocky site in the Australian tropics: Making the best of a bad lot

Most animals select nest sites non‐randomly, reflecting benefits of specific locations or incubation conditions for offspring viability as well as risks or costs to the reproducing adult. If few or no available nest sites offer suitable conditions, we expect animals to make the best of a bad lot, by selecting nest sites that provide the best conditions available. In tropical north‐western Australia, freshwater crocodiles (Crocodylus johnstoni: Crocodylidae) in a large artificial lake (Lake Argyle) experience this challenge: the types of nest sites used by this species in other parts of its range (moist, shaded sandy soils, far from the water's edge) are scarce. Measurements of 89 crocodile nests and 89 test holes (abandoned attempts at nesting) at Lake Argyle, and 28 nests on the nearby Ord River, show that most areas along the lakeshore are too steep and rocky for nesting. Crocodiles at the lake therefore are forced to nest at sites that are sun‐exposed, in dry gravelly substrates, and close to the water's edge. Comparisons of test holes and actual nests within such areas show that nesting crocodiles actively select sites that are less rocky, are suitable hydrically, and that provide stable thermal regimes. Those hydric and thermal attributes allow successful development of the offspring. The ability of freshwater crocodiles in Lake Argyle to flexibly modify their nest‐site selection criteria, under severe constraints enforced by this open rocky landscape, are critical to the species' success in exploiting the opportunity created by the dam's construction.     

Predators at bird nests in a northern hardwood forest in New Hampshire

ABSTRACT.   Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure.