Temporal Variation in Decisions about Parental Care in Bluegill, Lepomis macrochirus

Parental investment theory states that an individual will trade‐off present and future reproductive potential to maximize lifetime reproductive success. Only when parental care is costly in terms of reduced future reproductive potential should individuals be sensitive to changes in the value of current offspring and adjust their care. Here, we examine temporal variation in parental care decision‐making in bluegill (Lepomis macrochirus), in which care is provided by males called ‘parentals’. Previous research has shown that parentals that nest early in the breeding season are in higher energetic condition than those that nest later, and early nesting males appear not to pay an opportunity cost to their care in terms of reduced future reproductive potential. Early nesting males also may have higher paternity in their broods than later nesting males. To examine the parental care decisions made by early and mid‐season nesting parentals, we experimentally reduced males’ perceived paternity by swapping eggs between nests. We found that experimental males that nested early in the breeding season adjusted their brood defence behaviour similarly to control males, which had sham egg swaps performed. Conversely, experimental males that nested mid‐season significantly decreased their brood defence behaviour after the manipulation as compared with control males. Thus, unlike mid‐season nesting males, early nesting males appear relatively insensitive to changes in brood value (paternity), possibly because early nesting males pay little cost in terms of reduced future reproductive potential to providing full care or because these males have a predisposition to high paternity.     

Colonial Nesting and the Importance of the Brood Size in Male Parasitic Reproduction of the Mediterranean Damselfish Chromis chromis (Pisces: Pomacentridae)

We investigated male parasitic spawning in a protected natural population of Mediterranean damselfish. Chromis chromis nested in colonies, inside which males showed a high variability in mating success. Our field observations indicate that the egg batches obtained by the most successful fish were five times bigger than the ones obtained by the less successful fish and many males never received ovipositions. On the other hand, reproductive parasitism was a common tactic within the colony. Successful nesting males sneaked into their neighbours' nests depending on the amount of eggs in their nest, with small clutch size inducing the males to parasitic reproduction. Males failing to receive egg depositions on their nests showed a significantly higher parasitism rate than successful males. Non-territorial males occupied stations in the water column above the breeding grounds and whenever the opportunity arose, they disrupted spawning in progress, stealing copulation with females. We observed that the likelihood of males being parasitized by sneakers was not correlated with the size of their own clutch; on the contrary, it depended both on the number of neighbouring nests and on the number of neighbouring males with barren nests (i.e. unsuccessful males). No correlation was found between parasitic behaviour and male size, suggesting males may switch between spawning in their own and in their neighbour's nests depending on mating opportunity. The hypothesis that colonial nesting facilitates parasitic reproduction is here discussed.     

A trade-off generated by sexual conflict: Mediterranean wrasse males refuse present mates to increase future success

A variety of mechanisms, including intrasexual competition,intersexual conflict, and physiological constraints, can explainpatterns of reproduction and the adaptive value of specificbehaviors. In a Mediterranean wrasse, Symphodus ocellatus (Labridae),large, nesting males occasionally refuse to spawn with willingfemales in the presence of small, sneaker males. We exploredthe possible adaptive significance of this behavior. Nestingmales refuse females despite the fact that it reduces theirimmediate mating success. This nesting-male behavior also decreasesfemale and sneaker mating success and occurs when sneaker malessurround the nest. Experiments that decreased the number ofsneakers around nests showed that nesting males respond immediatelyto mating opportunities when fewer sneakers are present, andthus they are not simply constrained by a lack of energy orlack of sperm. Experiments that increased the number of sneakersat the nest caused nesting males initially to refuse spawningopportunities, followed by a subsequent decrease in sneakerpresence and an increase in mating rate. We propose that thisbehavior is the result of a trade-off between immediate matingsuccess and future reproduction created by competition betweenmales and conflict between the sexes. Males reduce their immediatemating success by reducing spawning at the nest; sneaker malessubsequently leave, and this decreases mate competition forthe nesting male. Unresponsiveness of nesting males also causessexual conflict between females and nesting males over mating.We argue that this behavior and the existence of a trade-offcan only be understood by examining intersexual conflict andintrasexual competition simultaneously.     

Simultaneous spawning by female stream goby Rhinogobius sp. and the association with brood cannibalism by nesting males

A laboratory experiment was conducted by varying the undersurface area of nesting substratum and the number of females in an experimental tank to elucidate the determinants of the mating pattern in the stream goby, Rhinogobius sp. cross‐band type. Males with larger nests tended to attract two or more females to their nest in a tank. Moreover, males spawned simultaneously with multiple females and entire brood cannibalism by males was rarely observed under a female‐biased sex ratio. When males spawned with a single female with low fecundity, however, entire brood cannibalism occurred at a high frequency, suggesting that a male guarding a nest with fewer eggs consumes the brood. Therefore, spawning behaviour of females that leads to a large egg mass would decrease the risk of entire brood cannibalism. In this species, simultaneous spawning by multiple females in a nest serves as a female counter‐measure against entire brood cannibalism. These results suggest that a conflict of interest between the sexes through brood cannibalism is a major determinant of simultaneous spawning.     

Sex differences in resource utilization by the peacock blenny

This paper presents data on the seasonal variation of gonadosomatic, hepatosomatic and feeding indices in nesting males, females and female-like males of the blenniid fish Salaria pavo . Eviscerated condition factors, female fecundity and feeding rates are also presented. The results are consistent with the hypothesis that females maximize their feeding rates during reproduction, converting food into eggs through repeated spawning. Nesting males feed at a very low rate during the breeding season. It is argued that one major component of the reproductive costs in these males is the reduction of feeding opportunities. Female-like males present lower reproductive costs, which probably reflects the compromise between fertilizing some eggs and growing.     

Male‐skewed adult sex ratio,survival, mating opportunity and annual productivity in the Snowy Plover Charadrius alexandrinus

Sex differences in adult mortality may be responsible for male‐skewed adult sex ratios and male‐skewed parental care in some birds. Because a surplus of breeding males has been reported in serially polyandrous populations of Snowy Plover Charadrius alexandrinus, we examined sex ratio, early‐season nesting opportunities, adult survival and annual reproductive success of a Snowy Plover population at Monterey Bay, California. We tested the hypotheses that male adult survival was greater than female survival and that a sex difference in adult survival led to a skewed adult sex ratio, different mating opportunities and different annual productivity between the sexes. Virtually all females left chicks from their first broods to the care of the male and re‐nested with a new mate. As a result, females had time to parent three successful nesting attempts during the lengthy breeding season, whereas males had time for only two successful attempts. Among years, the median population of nesting Plovers was 96 males and 84 females (median difference = 9), resulting in one extra male per eight pairs. The number of potential breeders without mates during the early nesting period each year was higher in males than in females. Adult male survival (0.734 ± 0.028 se) was higher than female survival (0.693 ± 0.030 se) in top‐ranked models. Annually, females parented more successful clutches and fledged more chicks than their first mates of the season. Our results suggest that in C. alexandrinus a sex difference in adult survival results in a male‐skewed sex ratio, which creates more nesting opportunities and greater annual productivity for females than for males.     

The Effect of an Experimental Brood Reduction on Male Desertion in the Panamanian Blue Acara Cichlid Aequidens coeruleopunctatus

Investment in present vs. future reproduction is a life-history trade-off faced by many animals. Because males generally pay a higher cost from lost mating opportunities than females, males are expected to react more strongly to changes in brood value. We examined the effect of an experimental brood reduction on male desertion in the substrate-brooding biparental cichlid Aequidens coeruleopunctatus under field conditions. We tested the prediction that brood reduction should decrease the duration of male care and examined the effect of brood reduction on the quality of male and female parental care. Our results show that males with reduced broods stopped providing parental care earlier than males with control broods. Males with reduced broods, however, also stayed longer with their broods as the season progressed. Brood reduction did not decrease daily investment in male or female parental care. We conclude that males trade off present and future reproduction by changing the duration but not the quality of parental care. The longer duration of male care in the experimental group later in the season suggests that the trade-off between present and future reproduction changes as the season progresses because the payoffs of desertion progressively decrease.     

Sperm traits in relation to male quality in colonial spawning bluegill

Sperm traits (morphology, motility and concentration within ejaculates) and various correlates of male quality (age, body condition, spawning location and timing) were studied in bluegill Lepomis macrochirus , breeding in both the interior and periphery of six colonies in Lake Opinicon, Ontario, Canada. Sperm traits varied significantly more among than within males suggesting that some aspect of male phenotype might influence sperm morphology and behaviour. No measures of male body condition or size were correlated with any sperm or ejaculate traits, when controlling statistically for confounding variables. Sperm swimming speed increased significantly with male age and varied significantly among spawning bouts (controlling for sperm tail length) suggesting that some unknown aspects of male quality might influence the fertilization capacity of spermatozoa. Sperm concentration in ejaculates was significantly higher in males nesting in the interior rather than the periphery of a colony suggesting that those males might also have higher fertilization capacity correlated with their superior dominance status or the lower risk of sperm competition. Thus, older males nesting in the interior of a colony during the first spawning bout of the season are expected to be the best sperm competitors in this population, but the physiological reasons for this increased fertilization capacity remain unknown.     

No Correlation Between Song and Circulating Testosterone Levels During Multiple Broods in the Domesticated Canary (Serinus canaria)

In anticipation of the breeding season male songbirds of the temperate zones undergo gonadal recrudescence in early spring that lead to elevated circulating testosterone (T) levels, positively correlated with an increase in aggressive and song behaviour. However, besides seasonal changes there are also marked fluctuations of T levels and song production within the breeding season. In many species, T levels and singing activity drop after pairing or after the first clutch is laid. Domesticated canaries (Serinus canaria) are multiple‐brooded with an extended breeding season, and males continue to sing after egg‐laying. So far, studies have mainly focused on the seasonality of T levels and song behaviour whereas the pattern of change throughout the breeding period is unknown. Here, we focused on the first and on the last brood of the breeding season. We measured plasma T levels in males at the different breeding stages and assessed song characteristics of males at both times. T levels fluctuated significantly throughout brood 1, being highest during the nest building stage compared with egg‐laying and feeding of young. No such changes occurred during the last brood. Temporal song characteristics changed between brood 1 and brood 3 with song length being the main contributor to explain these changes. Our data suggest that T mainly plays a role in mate attraction and initial nesting site selection but that elevated levels are not necessary for subsequent breeding attempts. Furthermore, temporal song characteristics are maintained independently of T levels, suggesting a threshold effect. Our results demonstrate behavioural and physiological plasticity of domesticated canaries during the breeding season and are consistent with previous findings in wild songbirds.     

Plasma levels of androgens and cortisol in relation to breeding behavior in parental male bluegill sunfish, Lepomis macrochirus

Like many teleosts, male bluegill sunfish (Lepomis macrochirus) provide sole parental care. To understand some of the proximate costs of parental care, we measured body condition and plasma levels of testosterone (T), 11-ketotestosterone (11KT) and cortisol in nesting bluegill males during pre-spawning, spawning and parental care stages. T and 11KT were at their highest mean levels during the pre-spawning period and decreased to lower levels early during the parental care period before rising again when the eggs hatched. Cortisol levels fluctuated across the breeding stages, but there was a noticeable increase from low levels on the day of spawning during the first 2 days of parental care when egg fanning is most intense. Levels of all hormones varied considerably among males, with androgen levels often correlating positively with a male's body condition. We also demonstrate, using a brood reduction experiment and repeated sampling of known individuals, that the presence of eggs affects hormone levels shortly after eggs hatch. Parental males in better body condition had higher levels of androgens during parental care. Males that were known to renest later in the season also had higher androgen levels and were in better body condition during the first nesting bout than males only known to have nested once. However, circulating levels of cortisol did not differ significantly between these groups. We discuss our findings in the context of proximate and ultimate costs of parental care and propose several reasons why elevated androgen levels may not be as incompatible with the expression of paternal care in male teleosts, as compared with avian and mammalian fathers.     

Factors affecting mate desertion by males in free-ranging convict cichlids (Cichlasoma nigrofasciatum)

Convict cichlid fish have biparental care for a period of about6 weeks lasting from egg laying until the young (fry) have grownto about 10 mm. However, the young can sometimes survive withcare from only one parent, and desertion of the mate and offspringby males has been observed. I tested a theoretical model modifiedfrom Lazarus (1990) which predicted that mate and offspringdesertion by male convict cichlids should be promoted by lowpredation pressure on fry, high remating opportunities for males,increasing age of fry, and decreasing number of fry. Males deserted7.8% of 334 broods studied during two breeding seasons in CostaRican streams. As predicted, males deserted their broods mostfrequently at sites with the highest brood survivorship (lowestbrood predation pressure), when fry were close to independenceand when brood size was smaller than average. Sex ratios andinterspawning intervals did not indicate any relationship betweenmate desertion and opportunities for remating for males. Thereuse of spawning caves may favor fidelity to the mate and brood,and defending the young from predators at the same time as defendingthe cave from conspecifics may favor biparental care in thisspecies.     

Brood desertion and polygamous breeding in the Kentish Plover Charadrius alexandrinus

In the Kentish Plover Charadrius alexandrinus one of the adults, typically the female, deserts the brood when the chicks are a few days old. Once parental care is terminated, adults may initiate a second nesting attempt if sufficient time remains within the season. For these nests, individuals pair with different mates from those of the first nesting attempt, thus becoming sequentially polygamous. In a small population of Kentish Plovers in Fuente de Piedra lake (southern Spain), the duration of biparental care of broods was longer than in other localities. It also showed considerable variation between years that was evidently related to Gull-billed Tern Gelochelidon nilotica predation pressure on the chicks. There was year-to-year variation in the number of polygamous matings. Both the duration of the breeding season and nesting success in the first half of the season limited the occurrence of polygamy. Despite females deserting broods earlier than males, the interval between the first and second nesting of polyandrous females and polygynous males was similar. The interval was not affected by the body condition of females after the first nesting attempt, nor by problems related to egg formation ability, but was probably due to the availability of potential mates. More females than males initiated second nests, suggesting that polygamous opportunities were more limited for males than for females. In terms of delayed breeding, reduced survivorship or reduced breeding opportunities in years following polygamous breeding, polygamous individuals did not have greater costs than non-polygamous ones. Females with second nests did not seem to be selective in mate choice, mating with any available male. Mates for second nests may therefore be of lower quality than those for first nests, as judged by male plumage characteristics. Clutch sizes and egg characteristics of polyandrous females were similar in first and second nests. Nest success of second nests was only 40% of that of first ones, with nest desertion accounting for 60% of the losses. As the costs of polygamy are apparently low and as breeding success is very variable among years, polygamous breeding of the long-lived Kentish Plover may be an important breeding strategy with which to increase individual lifetime reproductive success.     

American Kestrel reproduction: evidence for the selection hypothesis and the role of dispersal

Many hypotheses attempt to explain why younger, less experienced birds have a relatively low reproductive output. We evaluated reproductive patterns of marked American Kestrels Falco sparverius nesting in boxes in southwestern Idaho from 1992 to 2006 to test predictions of these hypotheses. Results were consistent with the selection (differential mortality) hypothesis and did not support the constraint, restraint or recruitment hypotheses. Most known-age Kestrels nested in their first year of life, and there was no apparent short-term or long-term reproductive advantage to delayed breeding. The number of years that Kestrels nested in study area boxes ranged from 1 to 6 years, with most Kestrels nesting in only 1 year. Reproductive rates were higher for birds with at least 1 year of nesting experience than for birds nesting in boxes for the first time. After 2 years of nesting, reproductive rates levelled off; there was no evidence for additional improvement or for senescence. Differences in reproductive output with experience/age were due to variation among and not within individuals. Individuals that nested in more than 1 year had similar reproductive rates in their first and second years. Poor producers either died or dispersed after 1 year of nesting in study area boxes. Successful females that nested early in the season and successful males that had been produced locally had the highest probability of returning to nest in a subsequent year.     

Late‐breeding Great Cormorants Phalacrocorax carbo sinensis produce fewer young of the more vulnerable sex

We examined the brood sex ratio and offspring body mass in relation to the timing of breeding and brood size in the Great Cormorant Phalacrocorax carbo sinensis. The brood sex ratio was not related to brood size but it was significantly related to the hatching date, with a decreasing proportion of males in the brood in the course of the season. Male chicks had significantly lower body mass if they hatched later in the season, whereas there was no such relationship for female offspring. Assuming that environmental conditions deteriorate with progress of the breeding season, and male offspring may be more vulnerable to poor environmental conditions, the observed decline in the proportion of male offspring late in the season may be adaptive.     

Simultaneous polygyny of the gobiid fish Asterropteryx semipunctata in relation to mate availability

Nesting males of Asterropteryx semipunctata conducted spawning behavior with 2–6 females simultaneously. We carried out field observations on a rocky reef in Kagoshima, Japan, to examine the hypotheses that large males will show multi-female spawning behavior because of their mating advantage, and that simultaneous multi-female spawning will occur when the operational sex ratio (OSR; the ratio of receptive males to receptive females) becomes female-biased. Contrary to our prediction, neither the total number of multi-female spawnings during a spawning season nor mean number of spawning females at a time were correlated with nesting male sizes. This indicates that larger males often did not conduct multi-female spawnings. As predicted, the incidence of multi-female spawning followed the change in the OSR over time—as the OSR in the study area became biased toward females, the incidence of multi-female spawnings gradually increased. Our results suggest that mate availability affects mating patterns in A. semipunctata.     

Residency Time as an Indicator of Reproductive Restraint in Male Burying Beetles

The cost of reproduction theory posits that there are trade-offs between current and future reproduction because resources that are allocated to current offspring cannot be used for future reproductive opportunities. Two adaptive reproductive strategies have been hypothesized to offset the costs of reproduction and maximize lifetime fitness. The terminal investment hypothesis predicts that as individuals age they will allocate more resources to current reproduction as a response to decreasing residual reproductive value. The reproductive restraint hypotheses predicts that as individuals age they will allocate fewer resources to current reproduction to increase the chance of surviving for an additional reproductive opportunity. In this study, we test for adaptive responses to advancing age in male burying beetles, Nicrophorus orbicollis. Burying beetles use facultative biparental care, but the male typically abandons the brood before the female. Previous work in male burying beetles has suggested several factors to explain variation in male residency time, but no study has observed male behavior throughout their entire reproductive lifetimes to determine whether males change residency time in an adaptive way with age. We compared residency time of males that reproduced biparentally, uniparentally, and on different-sized carcasses to determine if they used an adaptive reproductive strategy. Males did not increase residency time as they aged when reproducing biparentally, but decreased residency time with age when reproducing uniparentally. A decrease in parental care with age is consistent with a reproductive restraint strategy. When female age increased over time, males did not increase their residency time to compensate for deteriorating female condition. To our knowledge, this is the first test of adaptive reproductive allocation strategies in male burying beetles.     

Timing of current reproduction directly affects future reproductive output in European coots

Life-history theory suggests that the variation in the seasonal timing of reproduction within populations may be explained on the basis of individual optimization. Optimal breeding times would vary between individuals as a result of trade-offs between fitness components. The existence of such trade-offs has seldom been tested empirically. We experimentally investigated the consequences of altered timing of current reproduction for future reproductive output in the European coot (Fulica atra). First clutches of different laying date were cross-fostered between nests, and parents thereby experienced a delay or an advance in the hatching date. The probability and success of a second brood, adult survival until and reproduction in the next season were then compared to the natural variation among control pairs. Among control pairs the probability of a second brood declined with the progress of season. Delayed pairs were less likely and advanced pairs were more likely to produce a second brood. These changes were quantitatively as predicted from the natural seasonal decline. The number of eggs in the second clutch was positively related to egg number in the first clutch and negatively related to laying date. Compared to the natural variation, delayed females had more and advanced females had fewer eggs in their second clutch. The size of the second brood declined with season, but there was no significant effect of delay or advance. Local adult survival was higher following a delay and reduced following an advance. The effect of the experiment on adult survival was independent of sex. Laying date and clutch size of females breeding in the next year were not affected by treatment. The study demonstrates the existence of a trade-off between increased probability of a second brood and decreased parental survival for early breeding. Timing-dependent effects of current reproduction on future reproductive output may thus play an important role in the evolution of the seasonal timing of reproduction.     

Climate effects on nesting phenology in Nebraska turtles

A frequent response of organisms to climate change is altering the timing of reproduction, and advancement of reproductive timing has been a common reaction to warming temperatures in temperate regions. We tested whether this pattern applied to two common North American turtle species over the past three decades in Nebraska, USA. The timing of nesting (either first date or average date) of the Common Snapping Turtle (Chelydra serpentina) was negatively correlated with mean December maximum temperatures of the preceding year and mean May minimum and maximum temperatures in the nesting year and positively correlated with precipitation in July of the previous year. Increased temperatures during the late winter and spring likely permit earlier emergence from hibernation, increased metabolic rates and feeding opportunities, and accelerated vitellogenesis, ovulation, and egg shelling, all of which could drive earlier nesting. However, for the Painted Turtle (Chrysemys picta), the timing of nesting was positively correlated with mean minimum temperatures in September, October, December of the previous year, February of the nesting year, and April precipitation. These results suggest warmer fall, and winter temperature may impose an increased metabolic cost to painted turtles that impedes fall vitellogenesis, and April rains may slow the completion of vitellogenesis through decreased basking opportunities. For both species, nest deposition was highly correlated with body size, and larger females nested earlier in the season. Although average annual ambient temperatures have increased over the last four decades of our overall fieldwork at our study site, spring temperatures have not yet increased, and hence, nesting phenology has not advanced at our site for Chelydra. While Chrysemys exhibited a weak trend toward later nesting, this response was likely due to increased recruitment of smaller females into the population due to nest protection and predator control (Procyon lotor) in the early 2000s. Should climate change result in an increase in spring temperatures, nesting phenology would presumably respond accordingly, conditional on body size variation within these populations.     

SEASONALITY OF MARABOU STORKS LEPTOPTILOS CRUMENIFERUS IN EASTERN AFRICA

Nesting by Marabou Storks in eastern Africa is seasonal, and so are assemblages of non-breeding birds at places with a regular supply of food. In Uganda, where temperatures and day-length are almost constant, Marabous have nested at about the same time each year, despite considerable variations in rainfall from year to year. However, rainfall can have a modifying effect, delaying egg-laying by up to a few weeks. The timing of egg-laying varied regionally throughout eastern Africa, but in general nesting began during a dry season and continued into the next wet season. In drier areas the timing of nesting was more complex. Regional variations in the nesting season, and in the sizes of feeding assemblages, are consistent with north-south movements of individual Marabous to or across the equator, enabling them to avoid the late wet season and early dry season. These are times when the supply of natural foods is likely to be least. Figure 6 summarizes the data and indicates probable movements. In the wetter areas the main northwards movement is in October-November, returning four to six months later. In driet areas the timing is almost reversed.