The role of progeny quality and male size in the nesting success of smallmouth bass: integrating field and laboratory studies

Smallmouth bass display size-specific variation in reproductive success with larger brood-guarding males in a population more likely to rear offspring to independence than smaller individuals. The exact mechanisms responsible for this size-specific increase in reproductive output have yet to be identified. To assist in this process, we investigated the relationship between the size of brood-guarding male smallmouth bass and offspring quality (in this case, egg physiology, egg morphology, egg size, hatching success and lab survival). Further, we examined how factors such as egg physiology, egg morphology and egg size influenced reproductive success in the wild and hatching success in a controlled laboratory environment. Nesting male smallmouth bass that successfully reared their offspring to independence spawned earliest in the nesting period were the largest individuals, and guarded eggs with greater concentrations of cortisol compared to males that abandoned their offspring prematurely. Offspring survival in the laboratory was not correlated with offspring survival in the wild, indicating that caution should be used interpreting studies that attempt to relate laboratory-derived survival metrics to the wild. Together, results demonstrate size-specific differences in offspring quality for nesting smallmouth bass, which are correlated with higher concentrations of cortisol in eggs. However, hatching success under laboratory conditions was dissimilar to nesting success in the field relative to cortisol concentrations.     

Mating success in brood-guarding male rock bass,Ambloplites rupestris: the effect of body size

Synopsis The hypothesis that variation in a paternal trait associated with offspring survival will result in female mate choice based on that trait was tested in rock bass,Ambloplites rupestris, a temperate fresh water fish with uniparental male care. The number of eggs acquired by 108 nesting male rock bass, in Cranberry Lake (New York State, U.S.A.), was estimated in two different spawning episodes that differed in the size structure of the nesting male stock. Early breeders (between the 4–7 June 1989) were mainly medium and large males (101–300 g), as compared to late breeders (between the 19–21 June 1989) which were mostly small (50–100 g). Because survival of larvae in rock bass is significantly lower in nests guarded by small males as compared to nests guarded by medium and large males, it was hypothesized that female mate choice should have been (1) size-based, and (2) more intense late in the season when the nesting stock was comprised mostly of small males. The results were consistent with these hypotheses. Variation in egg numbers per nest was significantly higher during the late spawning episode. In addition, egg number per nest were normally distributed during the early spawning episode, but were positively skewed and leptokurtic during the later episode. The correlation between male size and egg number was significant for both spawning episodes. However, during the late episode male size explained 23% of the variation in egg numbers versus only 8% of the variation during the earlier episode.     

Male reproductive competition in spawning aggregations of cod (Gadus morhua, L.)

Reproductive competition may lead to a large skew in reproductive success among individuals. Very few studies have analysed the paternity contribution of individual males in spawning aggregations of fish species with huge census population sizes. We quantified the variance in male reproductive success in spawning aggregations of cod under experimental conditions over an entire spawning season. Male reproductive success was estimated by microsatellite-based parentage analysis of offspring produced in six separate groups of spawning cod. In total, 1340 offspring and 102 spawnings distributed across a spawning season were analysed. Our results show that multiple males contributed sperm to most spawnings but that paternity frequencies were highly skewed among males, with larger males on average siring higher proportions of offspring. It was further indicated that male reproductive success was dependent on the magnitude of the size difference between a female and a male. We discuss our results in relation to the cod mating system. Finally, we suggest that the highly skewed distribution of paternity success observed in cod may be a factor contributing to the low effective population size/census population size ratios observed in many marine organisms.     

Intraguild predation between spawning smallmouth bass (Micropterus dolomieu) and nest‐raiding crayfish (Orconectes rusticus): implications for bass nesting success

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Annual variation in parental care in smallmouth bass,Micropterus dolomieu

Synopsis An eight year field study is summarized outlining variation in parental care in a northern population of smallmouth bass. Nesting makes ranged in age from 4 to 12 + years old and ranged in size from 21 cm to 40 + cm in fork length. The age and size distributions were skewed right when strong year-classes entered the nesting stock. Larger makes had more offspring in their nests than smaller makes. The year-to-year variation in the duration of care was large and appears to be related to two general effects of water temperature. First, there was a significant positive relationship between the variation in spring spawning date and variation in the duration of parental care prior to swim-up of the larvae. This reflects the general effect of spring warming rate on the timing of nesting in each year. Second, in most years, there was a significant positive relationship between male size and the duration of parental care prior to swim-up. This reflects the consistent inverse relationship between male size and the seasonal timing of spawning in this population. The offspring of large makes spawning early in a season take longer to develop than offspring of makes nesting late in season. There is no relationship in most years between male size and duration of care after swim-up. Other factors unrelated to water temperature may be important in determining the duration of care after swim-up. In particular, ontogenetic changes in juvenile behaviour and energy depletion in nesters may be two important factors affecting care duration.     

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 Influence of Maternal Quality on Brood Sex Allocation in the Small Carpenter Bee,Ceratina calcarata

In the twig‐nesting carpenter bee, Ceratina calcarata, body size is an important component of maternal quality, smaller mothers producing significantly fewer and smaller offspring than larger mothers. As mothers precisely control the sex and size of each offspring, smaller mothers might compensate by preferentially allocating their investment towards sons. We investigated whether variation in maternal quality leads to variation in sex allocation patterns. At the population level, the numerical sex ratio was 57% male‐biased (1.31 M/F), but the investment between the sexes was balanced (1.02 M/F), because females are 38% larger than males (1.28 F/M). Maternal body size explained both sex allocation pattern and size variation among offspring: larger mothers invested more in individual progeny and produced more female offspring than smaller mothers. Maternal investment in offspring of both sexes decreased throughout the season, probably as a result of increasing maternal wear and age. The exception to this pattern was the curious production of dwarf females in the first two brood cell positions. We suggest that the sex ratio distribution reflects the maternal body size distribution and a constraint on small mothers to produce small broods. This leads to male‐biased allocation by small females, to which large mothers respond by biasing their allocation towards daughters.     

Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

Offspring sex ratios at the termination of parental care should theoretically be skewed toward the less expensive sex, which in most avian species would be females, the smaller gender. Among birds, however, raptors offer an unusual dynamic because they exhibit reversed size dimorphism with females being larger than males. And thus theory would predict a preponderance of male offspring. Results for raptors and birds in general have been varied although population‐level estimates of sex ratios in avian offspring are generally at unity. Adaptive adjustment of sex ratios in avian offspring is difficult to predict perhaps in part due to a lack of life‐history details and short‐term investigations that cannot account for precision or repeatability of sex ratios across time. We conducted a novel comparative study of sex ratios in nestling Cooper's hawks (Accipiter cooperii) in two study populations across breeding generations during 11 years in Wisconsin, 2001–2011. One breeding population recently colonized metropolitan Milwaukee and exhibited rapidly increasing population growth, while the ex‐Milwaukee breeding population was stable. Following life‐history trade‐off theory and our prediction regarding this socially monogamous species in which reversed sexual size dimorphism is extreme, first‐time breeding one‐year‐old, second‐year females in both study populations produced a preponderance of the smaller and cheaper sex, males, whereas ASY (after‐second‐year), ≥2‐year‐old females in Milwaukee produced a nestling sex ratio near unity and predictably therefore a greater proportion of females compared to ASY females in ex‐Milwaukee who produced a preponderance of males. Adjustment of sex ratios in both study populations occurred at conception. Life histories and selective pressures related to breeding population trajectory in two age cohorts of nesting female Cooper's hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Cooper's hawks in Wisconsin.     

Investigating the genetic load of an emblematic invasive species: the case of the invasive harlequin ladybird Harmonia axyridis

Introduction events can lead to admixture between genetically differentiated populations and bottlenecks in population size. These processes can alter the adaptive potential of invasive species by shaping genetic variation, but more importantly, they can also directly affect mean population fitness either increasing it or decreasing it. Which outcome is observed depends on the structure of the genetic load of the species. The ladybird Harmonia axyridis is a good example of invasive species where introduced populations have gone through admixture and bottleneck events. We used laboratory experiments to manipulate the relatedness among H. axyridis parental individuals to assess the possibility for heterosis or outbreeding depression in F₁ generation offspring for two traits related to fitness (lifetime performance and generation time). We found that inter‐populations crosses had no major impact on the lifetime performance of the offspring produced by individuals from either native or invasive populations. Significant outbreeding depression was observed only for crosses between native populations for generation time. The absence of observed heterosis is indicative of a low occurrence of fixed deleterious mutations within both the native and invasive populations of H. axyridis. The observed deterioration of fitness in native inter‐population crosses most likely results from genetic incompatibilities between native genomic backgrounds. We discuss the implications of these results for the structure of genetic load in H. axyridis in the light of the available information regarding the introduction history of this species.     

An invasive gull displaces native waterbirds to breeding habitats more exposed to native predators

The effect of invasive opportunistic predators may include population changes in both native prey and native predators as well as alteration of predator–prey interactions. We analyzed the activity of native magpie Pica pica and changes in population, nest sites and nesting success probability of native waterbirds (namely: grebes, ducks, rails and native gulls) in response to the population growth of the invasive Caspian gull Larus cachinnans. The study was carried out at a reservoir in southern Poland and at a similar control reservoir where the Caspian gull was absent. Both the invasive gulls and the native magpie are opportunistic predators of nests of native waterbirds. The population increase of the invasive gull led to a decline in the population of native black-headed gulls Larus ridibundus only. However, the invasive gull displaced all the native species from the breeding islets located in the central part of the reservoir to islets located close to the shoreline. The latter were frequently visited by magpies, which depredated on nests along the shores, leading to an up to threefold decrease in nesting success as compared with nests located in the central area of the invaded reservoir. Predation by Caspian gulls was rarely observed. Thus, the invasion of Caspian gull caused complex direct and indirect effects on the waterbird community that included competition for breeding sites, changes in the spatial distribution of nests and alteration of predation rate by native predators. Moreover, the effects of invasion may not be reflected by changes in population size of native species.     

Sons do not take advantage of a head start: parity in herring gull offspring sex ratios despite greater initial investment in males

Skewed adult sex ratios sometimes occur in populations of free‐living animals yet the proximate mechanisms, timing of sex‐biases, and the selective agents contributing to skew remain a source of debate with contradictory evidence from different systems. We investigated potential mechanisms contributing to sex biases in a population of herring gulls with an apparent female skew in the adult population. Theory predicts that skewed adult sex ratios will adaptively lead to skewed offspring sex ratios to restore balance in the effective breeding population. Parents may also adaptively bias offspring sex ratios to increase their own fitness in response to environmental factors. Therefore, we expected to detect skewed sex ratios either at hatching or at fledging as parents invest differentially in offspring of different sexes. We sampled complete clutches (n = 336 chicks) at hatching to quantify potential skews in sex ratios by position in the hatch order, time of season, year, and nesting context (nest density), finding no departure from equal sex ratios at hatching related to any of these factors. Further, we sampled 258 chicks at near‐fledging to investigate potential sex biases in survival at the chick stage. Again, no biases in sex ratios were recorded. Male offspring were favored in this population via greater maternal investment in eggs carrying male embryos and greater parental provisioning of male offspring which reached greater sizes by fledging. Despite the advantages realized by male offspring, females were equally as likely to fledge as males. Thus, biased adult sex ratios apparently arise in the post‐fledging and pre‐recruitment stage in our population.     

Male mating success and female mate choice in the river sculpin,Cottus nozawae (Cottidae)

Synopsis Mating success of males and its correlates were investigated in a natural population of the polygynous fluvial sculpinCottus nozawae. Furthermore, the female mate preference of this species was examined experimentally under alternative conditions for mating in a stream. The mating success of individual males (the number of females with which a male mated) ranged between 0 and 8 with a mean of 2.41 in 1983 and 2.52 in 1989, in a population of which the sex ratio was about 1 : 2 in both years, skewed toward females. Mainly due to the excess of nests without egg masses and the few nests with one egg mass, the distribution of male mating success did not fit a Poisson distribution, indicating its non-randomness. Male mating success was not correlated either with the size of the nest rocks or with the male size, suggesting that these two variables are not determinants of mating success. The mate choice experiments demonstrated that females of this species more frequently chose smaller males as mates whose nests already contained eggs than large males without eggs. Additionally, an analysis of stomach contents of guarding males suggested that the parental males ate their own eggs during egg guarding (filial-cannibalism). Based on these results and on a comparison of reproductive characteristics with congeneric species, it is suggested that one of the most important determinants for female mate choice inCottus species may be whether or not parental males are filial egg cannibals.     

Correlates of reproductive success in stream-dwelling male rock bass,Ambloplites rupestris (Centrarchidae)

Synopsis Reproductive success was determined for individual male rock bass, Ambloplites rupestris, inhabiting the Middle Thames River near London, Ontario. Successful males produced numbers of young similar to rock bass breeding elsewhere, but the probability of males producing any young at all was comparatively small. Flooding, predation, and fouling of nests by algae were the major causes of brood mortality. Brood vulnerability was greatest within the egg, when nests were probably most conspicuous to predators. Male reproductive success was positively correlated with large size, early nesting, warm water conditions, and minimal flow rates. Larger males were chosen preferentially by females, and renested more often.     

Colony growth and reproductive ability of feral nests of the introduced bumblebee Bombus terrestris in northern Japan

The introduced Bombus terrestris has been blamed for the decline of native bumblebee populations in Japan. To control this invasive species, it is necessary to understand its ecological traits in its newly established range. Here, we investigated the colony growth pattern and reproductive ability of feral nests of B. terrestris in northern Japan from 2003 to 2006. Nests collected at various times showed initially slow growth followed by rapid development. This pattern is consistent with findings in previous studies using laboratory-raised colonies. Our results also suggested that protandrous colonies tend to specialize in male production, whereas protogynous colonies specialize in gyne production, producing a split sex ratio in feral colonies of B. terrestris. The numerical population sex ratio was 1.40 gynes per male, calculated from the numbers of pre-emergence cocoons for gynes and males, showing a female-biased sex ratio at the population level. Mature colonies produced a mean of 376.5 cocoons and 90.2 gyne cocoons (22.1% of the total). The proportion of gynes produced by B. terrestris nests exceeded both those of conspecifics observed in other countries and those of consubgeneric native Japanese species. The propagule pressure hypothesis appears to explain the probability of establishment of this invasive species. Suitable nest sites for B. terrestris queens appeared to be in short supply, and B. terrestris may win usurpation contests against native species due to its large size, resulting in the decline of native bumblebee species.     

Turtle mating patterns buffer against disruptive effects of climate change

For organisms with temperature-dependent sex determination (TSD), skewed offspring sex ratios are common. However, climate warming poses the unique threat of producing extreme sex ratio biases that could ultimately lead to population extinctions. In marine turtles, highly female-skewed hatchling sex ratios already occur and predicted increases in global temperatures are expected to exacerbate this trend, unless species can adapt. However, it is not known whether offspring sex ratios persist into adulthood, or whether variation in male mating success intensifies the impact of a shortage of males on effective population size. Here, we use parentage analysis to show that in a rookery of the endangered green turtle (Chelonia mydas), despite an offspring sex ratio of 95 per cent females, there were at least 1.4 reproductive males to every breeding female. Our results suggest that male reproductive intervals may be shorter than the 2-4 years typical for females, and/or that males move between aggregations of receptive females, an inference supported by our satellite tracking, which shows that male turtles may visit multiple rookeries. We suggest that male mating patterns have the potential to buffer the disruptive effects of climate change on marine turtle populations, many of which are already seriously threatened.     

Phenotypic variability in nesting success among Osmia lignaria propinqua females in a glasshouse environment: (Hymenoptera: Megachilidae)

Abstract. 1. The phenotypic variability of several estimates of fitness among seventeen nesting female O.lignaria Cresson was examined in a glasshouse provided with abundant resources.
2. Females exhibited wide variation in: (a) number of nests and cells made and in their rate of construction, (b) the incidence of mortality of offspring, and (c) the percentage of male offspring produced (52–100%).
3. In confirmation of earlier field studies: (a) more offspring of both sexes were produced during the first half of the nesting season, (b) most female offspring were produced early in the nesting season, (c) most parental investment during the last half of the flight season was made in male offspring, (d) there was a decrease in offspring size with season, with females decreasing more than males, and (e) the ratio of female/male body weight was = 1.8. These results appear to be due to ageing rather than to a reduction in resource availability.
4. No relation between female size and fecundity was evident.
5. There was no evidence that small females tended to produce a greater proportion of the smaller sex (males) than did large females.
6. Smaller offspring of both sexes had a much greater probability of dying overwinter than did large offspring. However, where the sexes overlapped in size (large males, small females), almost all females died and almost all males survived. We hypothesize that as size of offspring produced declines with season, a greater proportion of males are produced because they have a much greater probability of surviving at small body sizes.     

‘Harem’ and ‘non-harem’ type mating systems in two species of subsocial spider mites (Acari,Tetranychidae)

The mating system of a subsocial spider mite, Schizotetranychus miscanthi Saitō, which is closely related to Schizotetranychus longus Saitō (the long seta form of Schizotetranychus celarius (Banks) is a synonym of the latter) was studied in comparison with that of S. longus. Comparisons between nesting patterns of the two related species, S. miscanthi and S. longus revealed a difference in distribution of males among nests. Although more than one male sometimes occurred in the large nests of S. miscanthi, most nests were occupied only by a single male. On the other hand, many nests of S. longus included several males. Behavioral experiments revealed that the male and females of S. miscanthi which cohabited in a nest defended their offspring from phytoseiid predators. Observations and a census of the nesting pattern in a wild population indicate that this is the second example of biparental defense and of a subsocial life-pattern in spider mites. Differences in mating systems were experimentally demonstrated in the two species. Only a single male of S. miscanthi survived in a nest, as a result of highly aggressive male-male combat, while two males of S. longus cohabited in a nest. The mating system of the former species is thus considered as harem polygyny, while that of the latter as scramble type polygyny. Furthermore, observations by video recording and scanning electron microscopy showed that the winning male in the male-male combat in S. miscanthi often preyed on the loser, suggesting cannibalism among them.     

Recognition of non-native peacock bass, <Emphasis Type="Italic">Cichla kelberi</Emphasis> by native prey: testing the naiveté hypothesis

Prey naiveté is proposed as one of the main reasons behind species extinctions attributed to invasive predators. This study examined whether the naiveté hypothesis could explain extinctions after the introduction of peacock bass (Cichla kelberi) in Paraná River, Brazil. Our results show that prey responded to both visual and chemical cues of peacock bass. Displayed avoidance behaviors were equal to or greater than those observed with a native predator, Hoplias malabaricus. We conclude that lack of recognition was not responsible for the observed vulnerability of native species to this introduced predator. Finally, we discuss implications of these findings for the native biodiversity and convene other potential explanations for the observed effects of peacock bass on native prey.     

The rise and fall of local populations of ortolan buntings Emberiza hortulana: importance of movements of adult males

Changes in population size of local populations of birds have usually been interpreted in relation to adult return rate and recruitment of young individuals after natal dispersal. Little is known about the importance of redistribution of adult individuals through breeding dispersal. The small Norwegian population of ortolan buntings Emberiza hortulana has a patchy distribution with about 30 long‐term local populations. During a period of general population decline (29% decrease over 7 years), the population trends of local populations (measured as number of males recorded) were highly variable, with some even increasing four‐fold. Comparisons of demographic parameters showed that adult immigration rate (i.e. dispersal of adult males) explained both yearly changes in male population size and population trends over the whole study period better than adult return rate or adult emigration rate, or a measure of recruitment of young males. Adult immigration rates and recruitment rates were correlated, suggesting that both young and adult males find the same places attractive. In the study area, adult sex ratio was strongly male‐biased, and immigration rate was higher when local sex ratio was less skewed. In addition, less skewed sex ratio was related to higher adult return rate and lower emigration rate. We found no relationships between measures of breeding success and population change. We suggest that conspecific attraction may explain the observed patterns. Some local populations may act as hot‐spots attracting adult males from other populations. Thus, local population changes need not reflect overall population growth rate, but may be a consequence of redistribution of adult birds.     

Dynamics of nest defense by male centrarchid fish

Field observations were conducted on four species of nesting male centrarchids to determine if guarding males discriminate intruders with respect to their potential threat to the brood, their size or position in the water column, or by the stage of the nest. Results demonstrated that bluegill (Lepomis macrochirus) and pumpkinseed (L. gibbosus) sunfish were the most frequent intruders and were attacked the most often. Nest guarding male largemouth bass (Micropterus salmoides) attacked intruders further from the nest and had the highest probability of attack of the four species studied. Rock bass (Ambloplites rupestris) males had the shortest distance of attack and one of the lowest probabilities of attack. Male black crappie (Pomoxis nigromaculatus) and pumpkinseed were intermediate in both responses. For all species, the size of intruder did not influence attack distance but larger males had a greater attack distance than smaller males. The distance of attack was greatest during the period immediately after hatch. These findings indicate species-specific differences in nest defense and males did discriminate intruders, possibly on their potential threat to the brood. The defense of the nest was related to nest stage, a finding which supports current theory of parental care.