Females In Good Condition Research Articles

Effects of inbreeding and elevated rearing temperatures on strategic sperm investment.

Males often strategically adjust the number of available sperm based on the social context(i.e. sperm priming response), but it remains unclear how environmental and genetic factors shape this adjustment. In freshwater ecosystems, high ambient temperatures often lead to isolated pools of hotter water in which inbreeding occurs. Higher water temperatures and inbreeding can impair fish development, potentially disrupting sperm production. We used guppies (Poecilia reticulata) to investigate how developmental temperature (26 °C, 30 °C) and male inbreeding status (inbred, outbred) influence their sperm priming response. We also tested if sperm priming was affected by whether the female was a relative (sister) and whether she was inbred or outbred. There was no effect of rearing temperature; male inbreeding status alone determined the number of available sperm in response to female presence, her inbreeding status, and her relatedness. Inbred males produced significantly more sperm in the presence of an unrelated, outbred female than when no female was present. Conversely, outbred males did not alter the number of sperm available in response to female presence or relatedness. Moreover, inbred males produced marginally more sperm when exposed to an unrelated female that was outbred rather than inbred, but there was no difference when exposed to an inbred female that was unrelated versus related. Together, a sperm priming response was only observed in inbred males when exposed to an outbred female. Outbred females in our study were larger than inbred females, suggesting that inbred males strategically allocated ejaculate resources toward females in better condition.

Limited evidence of biased offspring sex allocation in a cavity-nesting conspecific brood parasite.

Sex allocation theory predicts that mothers should bias investment in offspring toward the sex that yields higher fitness returns; one such bias may be a skewed offspring sex ratio. Sex allocation is well-studied in birds with cooperative breeding systems, with theory on local resource enhancement and production of helpers at the nest, but little theoretical or empirical work has focused on birds with brood parasitic breeding systems. Wood ducks (Aix sponsa) are a conspecific brood parasite, and rates of parasitism appear to increase with density. Because female wood ducks show high natal philopatry and nest sites are often limiting, local resource competition (LRC) theory predicts that females should overproduce male offspring-the dispersing sex-when competition (density) is high. However, the unique features of conspecific brood parasitism generate alternative predictions from other sex allocation theory, which we develop and test here. We experimentally manipulated nesting density of female wood ducks in 4 populations from 2013 to 2016, and analyzed the resulting sex allocation of >2000 ducklings. In contrast to predictions we did not find overproduction of male offspring by females in high-density populations, females in better condition, or parasitic females; modest support for LRC was found in overproduction of only female parasitic offspring with higher nest box availability. The lack of evidence for sex ratio biases, as expected for LRC and some aspects of brood parasitism, could reflect conflicting selection pressures from nest competition and brood parasitism, or that mechanisms of adaptive sex ratio bias are not possible.

Female mate choice is affected by male condition but not female condition in an assassin bug

Abstract Sexual selection theory predicts that females prefer males in good condition because mating with them provides more resources such as sperm, ejaculates and nuptial gifts. The female's condition also affects her mating decisions, and condition‐dependent mate choice may allow her to gain more resources from a mate in the context of fluctuating resource availability. We here investigated how female mating decisions and their fitness consequences varied in the assassin bug Amphibolus venator when the conditions of potential mates and/or the females differed (good or poor condition). Females in both good and poor conditions preferred males in good condition, and females that mated with males in good condition produced more eggs with higher hatch rates. This increase in fitness may be attributed to the males in good condition transferring more ejaculate to the females. In contrast, female mate preference, fecundity and hatch rates were not affected by their own condition. This suggests that females do not choose mates according to their own condition in A. venator. However, the females in good condition laid larger eggs than females in poor condition, implying that females in good condition may invest more per egg to improve their reproductive success. To understand the evolution of female mate choice, it is necessary to investigate the effects of the condition of both sexes on female mating decision and their fitness. In A. venator, male condition may affect mate choice more than female condition.

Rapid species‐level hemolymph color test for all life stages of Nipaecoccus viridis (Newstead) (Hemiptera: Pseudococcidae), an invasive and regulatory pest in the United States

AbstractSlide‐mounting is mandatory for accurate morphological identification of mealybug species (Hemiptera: Pseudococcidae). A typical slide‐mounting process is performed in laboratory settings and requires several tedious and technical steps that can take up to 2 hr. Moreover, most of the taxonomic literature on mealybugs is based on adult females, whereas it can be difficult to find adult females in good condition in field samples. We tested 2,635 specimens of 57 mealybug species from 26 genera of Pseudococcidae collected from all over Florida for two consecutive years to discover an alternative to slide‐mounting specimens of Nipaecoccus viridis (Newstead), an emerging polyphagous pest of regulatory concern in the United States, now known to occur in Florida. Recent exceptionally high infestations in commercial citrus‐growing areas have activated regulatory agencies to implement quarantine and regulatory measures in efforts to halt its further spread within and outside of Florida. A 5‐min haemolymph colour test of eggs, immatures and adults is species‐specific to N. viridis. This test will allow for the identification of all life stages even when an adult female is not available. We discuss implementing this test in the field to help growers, researchers and regulators make preliminary identifications.

Compensatory effect of egg size dimorphism on hatching asynchrony in Magellanic penguin

Egg laying is one of the most important phases in a female bird's breeding cycle. Its cost is high because eggs contain all the resources needed for the development of an embryo. Variation in size and quality of eggs can have important long‐term consequences for offspring survival. Hatching asynchrony is known to influence sibling competition in many bird species. Last‐hatched chicks will have a competitive disadvantage throughout the pre‐fledgling period because they are smaller. The aim of this study was to analyze the effect of hatching asynchrony and egg size variation on the growth and fledging success of Magellanic penguin Spheniscus magellanicus chicks after disentangling the effects of parental condition. We simultaneously manipulated egg size dimorphism, hatching asynchrony and parental condition by performing a cross‐fostering experiment, creating broods with controlled egg size dimorphism and hatching asynchrony in a colony of Magellanic penguins located in Isla Quiroga, Santa Cruz, Argentina. We found that hatching asynchrony had a negative effect on last‐hatched chicks, but this disadvantage was mitigated by egg size dimorphism in their favor. Moreover, females in good condition invest more in second than in first chicks, which, added to a greater investment by foster fathers, leading to offspring fledging in good condition. On the contrary, for the first‐hatched chicks, we found that body condition of the biological father was an important factor for their growth. We conclude that raising more than one chick seems to be a decision based on parental condition throughout the breeding season.

Mutual mate choice and its benefits for both sexes

In mating interactions, it is common in nature for both sexes to choose simultaneously. However, this mutual mate choice and its consequences for progeny has received relatively little study; an approach where both male and female condition is manipulated is thus desirable. We compared both sexes’ preferences in Tenebrio molitor beetles when individual condition varied (healthy vs infected with a fungus), and observed the direct benefits of those preferences. We predicted that: (a) females and males in good condition would prefer high quality mates; (b) preferences would be weaker when the choosing individual is in poor condition (and thus less selective given, for example, time and energetic constrains); and, (c) high quality mates would lay a larger number of total eggs and/or viable eggs than low quality mates. We found that both males and females in good condition were not more likely to choose mates that were also in good condition. However, poor-condition animals were more likely to prefer similar quality animals, while high-condition animals did not necessarily prefer mates of similar condition. Choosing sick males or females had a negative impact on egg number and viability. Our results suggest a non-adaptive mate choice in this species. Possibly, a deteriorated condition may drive individuals to invest more in attracting mates, because their chances of surviving the infection are very low. However, we do not discount the possibility that the fungus is manipulating individuals to increase its transmission during mating.

Size, ornamentation, and flight feather morphology promote within-pair paternity in a sexually dimorphic passerine

Morphology in sexually dimorphic species is related to increased opportunity for sexual selection when traits reflect individual quality. In socially monogamous species, it may function to increase variance in reproductive success if exaggerated traits are related to the opportunity to engage in extra-pair paternity (EPP). Nonetheless, it is poorly understood if ornamental versus functional traits are differentially related to the distribution of paternity across individuals. We examined EPP in the Scissor-tailed Flycatcher (Tyrannus forficatus), a sexually dimorphic suboscine passerine, to determine how flight feather morphology (both ornamental and related to flight performance), ornamental coloration, and flight performance were related to paternity for males and females. We assessed paternity at 140 nests across 7 years and found that 73% of nests contained extra-pair young with 59% of nestlings resulted from extra-pair fertilizations. Males that secured paternity with their social mate had larger size (wing chord and tail length), better body condition, and more exaggerated ornamental traits (color, primary notch, and streamer length) than cuckolded males. When compared directly to the social males they cuckolded, however, cuckolders had shorter primary notches and had duller coloration. Elongated flight feather features were associated with greater maneuverability during flight, and longer primary notches and tail streamers were associated with maintenance of within-pair paternity, possibly via flight displays. Females that cuckolded their mates had less exaggerated flank coloration but better body condition than those that did not. We posit that in this system, there is a lack of strong selection on extra-pair mate morphology; rather, high-quality males maintained WPP while females in good condition were more likely to cuckold social males of poorer quality, signaling a role of reciprocal selection in extra-pair mate choice. Determinants of the frequency and extent of extra-pair paternity are central to our conception of mating systems, population genetics, and sexual selection. Morphological determinants can influence faithfulness to a mate and are a key aspect of locomotion, limiting or enhancing an individual’s ability to interact with others. We examined how ornamental (coloration and tail streamers) and functional traits involved in flight (wing and tail structure) correlated with cuckoldry. Male condition, size, and ornamental traits were negatively associated with cuckoldry; yet, social males were cuckolded by males of poorer quality. Flight feather characteristics were positively associated both with flight performance and maintenance of paternity, suggesting a role of flight in cuckoldry. Female body condition was related to cuckoldry and perhaps indicates reciprocal choice by males for healthy extra-pair mates. We posit a lack of strong selection on extra-pair mate morphology in this system; rather, high-quality males maintained WPP while females were more likely to cuckold social males of poorer quality.

Reproductive senescence in free-ranging North American elk Cervus elaphus Cervidae

Abstract Successful production of calves is necessary for growth of North American elk (Cervus elaphus Linnaeus 1758) populations, but few studies have evaluated age-related effects on both the conception and survival of a calf to weaning in multiple free-ranging populations. Conception and survival of calves to weaning were both affected by maternal age, with old (age 9 and older) females showing reproductive senescence as compared to prime-aged (ages 2–8) females despite achieving similar or greater size and condition. Reproductive senescence in our free-ranging populations ultimately resulted in old females weaning fewer calves (0.42 calves/female) than did prime-aged females (0.64 calves/female). Other factors, especially maternal size, also influenced conception and survival to weaning, and these interacted with age in a consistent manner, i.e. larger females or females in better condition were more likely to conceive and successfully wean calves within each age class. Female age structure receives less consideration in ungulate management than does male age structure, despite demonstrated impacts on population productivity of multiple species because of reproductive senescence. Because of the large proportion of individuals in senesced age classes in elk populations, low productivity in populations may simply reflect female age structure, rather than other frequently hypothesized factors.

Getting ready for the winter: Timing and determinants of molt in an alpine ungulate.

Because growth of new hairs entails energetic costs, individual condition and access to food should determine the timing of molt. Previous studies on the timing of molt in ungulates have mostly focused on the influence of age class and reproductive status, but the effects of body condition and environmental phenology have not been evaluated. Our goal was to assess how intrinsic traits and environmental conditions determine the timing of winter coat shedding in a mountain goat population monitored for 27 years. The date of molt completion followed a U shape with age, suggesting that senescence occurs in terms of the molting process in mountain goats. Juveniles of both sexes delayed molting in a similar fashion, but molt timing differed between sexes during adulthood. Males molted progressively earlier until reaching age when reproduction peaked, after which they started delaying molting again. Females reached earliest molt dates at age of first reproduction and then progressively delayed molt date. Lactating females molted 10 days later than barren females on average, but this only occurred in females in good condition. Thus, although it has been shown that reproduction delays molt in ungulates, our results indicate that body condition can override this effect. Overall, our results revealed that access to both extrinsic and intrinsic resources is one of the key mechanisms driving molting processes in a mammalian herbivore.

Variation in offspring development is driven more by weather and maternal condition than predation risk

Abstract Variation in offspring development is expected to be driven by constraints on resource allocation between growth and maintenance (e.g. thermoregulation). Rapid post‐natal development decreases predation risk to offspring, while inclement weather likely prolongs development. For taxa with parental care, parental behaviour may partially buffer offspring against extrinsic drivers like predation risk and severe weather. Using a 7‐year dataset from an alpine population of horned lark Eremophila alpestris, a ground‐nesting songbird in northern British Columbia, Canada, we investigated multiple potential drivers of variation in the duration of incubation and nestling development. Using path analysis, we evaluated the direct effects of weather, predation risk and parental care on offspring development, as well as indirect developmental “carry‐over” effects of conditions during incubation on the nestling period. Nestling period duration varied by nearly 100% (7–13 days) and incubation duration by 40% (10–14 days). Cold ambient temperatures late in the nestling period prolonged development by 1 day for every 2 days below 10°C, particularly when combined with heavy precipitation. Rapid nestling development was associated with high predation risk, and prolonging development incurred a nest survival cost (–2.3% per day). Females in good condition created nest environments that promoted rapid nestling development periods (average = 8–9 days) compared to poor condition females during harsh, early‐season conditions (10–11 days), indicating parental buffering capabilities against environmental constraints. Fledging age was weakly correlated with incubation duration (r = –0.21) suggesting minimal developmental carry‐over effects. Given high nest predation risk, immediate fitness benefits can be derived by overcoming environmental constraints and reducing development time. While predation risk was influential, inclement weather and maternal condition had stronger effects on variation in offspring development. Addressing multiple drivers of variation in key life‐history traits can provide important context for understanding life‐history theory under changing environmental conditions. A plain language summary is available for this article.

Are females in good condition better able to cope with costly males?

This work was supported by Australian Research Council (M.J.), the European Society for Evolutionary Biology (Hewitt Mobility Award 2017 to M.I.C.), and a TalentHub grant from the Agencia Andaluza del Conocimiento (S.Z.).

Parental Condition and Infant Sex at Birth in the Japan Environment and Children’s Study: A Test of the Trivers–Willard Hypothesis

The Trivers–Willard hypothesis predicts that females in good condition should bear more sons rather than daughters in certain mammals, including humans. This study tests the hypothesis by using 66,638 childbirth records from a national birth cohort survey in current Japan. Our analyses showed that, contrary to the hypothesis, indicators of parental condition, such as mother’s age, body mass index, job status, education level, medical history, or household income, had few statistically significant effects on infant sex at birth. In previous studies investigating the Trivers–Willard hypothesis, the results have been quite mixed and inconclusive. We discuss some theoretical and methodological challenges towards a precise understanding of the hypothesis in human populations.

Partible Paternity, the Secondary Sex Ratio, and a Possible Trivers-Willard Effect

Partible paternity, the belief that a child can have more than one biological father, is widespread in lowland South America. An analysis of demographic data sets from four lowland tribes (Ache, Bari, Ese Eja, and Surui) reveals a systematic variation in the sex ratios of live births with respect to the number of fathers to whom the births are attributed. Births attributed to only one father show a sex ratio that is unexceptional for South America; births with two fathers are highly male biased, while children with three or more fathers are female biased. This pattern may be a manifestation of a phenomenon predicted by the Trivers-Willard hypothesis, which proposes that, in many circumstances, females in good condition might bias their offspring toward males, whereas those in poor condition would produce a preponderance of females. If, as suggested below, a woman with a husband and a single extramarital lover tends to be better cared for before and during a pregnancy than other women, this difference might result in the improved maternal condition required by the Trivers-Willard hypothesis for excess males, whereas women who accept two or more lovers might be preponderantly those who are already in distress, thus tending to produce female-biased offspring.

Thrifty Females, Frisky Males: Winter Energetics of Hibernating Bats from a Cold Climate.

Mammalian hibernation consists of energy-saving torpor bouts (periods of controlled reduction in body temperature [Tb]) interspersed with brief arousals to normothermic Tb. Frequency and duration of torpor bouts and arousals can affect winter survival and are thought to be influenced by an optimization balancing the energetic benefits of prolonged torpor against the physiological and ecological costs (e.g., accumulation of metabolic wastes). Female little brown bats (Myotis lucifugus) spend their fat reserves more slowly than males during winter, presumably so they can emerge from hibernation in good condition to initiate pregnancy. We used temperature telemetry over three winters to test a prediction of the optimization hypothesis that female M. lucifugus would use longer torpor bouts and/or shorter arousals than males. Females did conserve energy relative to males by adjusting the magnitude and duration of arousals but not the duration of torpor bouts. Although torpor bout duration did not vary by sex for adults, it did vary by age. Adults initially used longer torpor bouts than young-of-the-year, but this difference declined as cave temperature warmed in spring. Males and females in better condition spent more energy during hibernation, again via increased arousal duration rather than decreased torpor bout duration. Longer arousals by males could increase reproductive fitness if males mate with torpid females throughout winter. Our results highlight demographic differences in winter behavior for small hibernators facing extreme energy limitation in cold climates and illustrate the influence that reproductive costs have on hibernation energetics.

Berry production drives bottom–up effects on body mass and reproductive success in an omnivore

Obligate herbivores dominate studies of the effects of climate change on mammals, however there is limited empirical evidence for how changes in the abundance or quality of plant food affect mammalian omnivores. Omnivores can exploit a range of different food resources over the course of a year, but they often rely on seasonally restricted highly nutritious fruiting bodies during critical life stages. Brown bears Ursus arctos in Sweden are dependent on berries for fattening before entering hibernation. We used a ten‐year time series to evaluate the effect of temperature and snow on annual variation in berry abundance and how this variation affected bears. We found marked interannual variation in berry production of bilberry Vaccinium myrtillus and lingonberry V. vitis‐idaea, that we could attribute in part to temperature during plant dormancy and flowering and precipitation during fruit ripening. Both, autumn weights of female bears and spring weights of yearling bears increased linearly with bilberry abundance. When bilberry abundance was low, lightweight female bears had a lower reproductive success than females in better condition. This effect vanished when food abundance was above average, indicating that lightweight females could compensate for their initial weight during good bilberry years. Our study highlights the importance of considering individuals’ dynamic responses to variation in food availability, which leave some more vulnerable to food shortage than others. Individual life‐history heterogeneity in response to resource variation likely affects long‐term population recruitment. Our findings emphasize that Scandinavian bears can be dependent on a single food resource during a critical period of the year and are therefore less resilient to environmental change than expected for an omnivore. Future climate scenarios predict ambiguous trends for weather covariates that affected crucial stages of berry phenology, preventing a clear prognosis of how climate change may affect long‐term bilberry production.

Size, season and offspring sex affect milk composition and juvenile survival in wild kangaroos

AbstractThe main component of mammalian maternal care is milk production. The composition of milk has been hypothesized to determine offspring survival, and to vary with offspring sex. Few studies, however, have examined variation in milk composition of wild mammals in seasonal environments, where environmental conditions can impact the ability of mothers to provide care. We investigated individual differences in milk composition and offspring survival in wild eastern grey kangaroos (Macropus giganteus). We analyzed total protein and lipid concentrations in 103 milk samples from 91 females over 2 years. In a year of low forage production, few females that lactated were in poorer condition and produced milk of lower energy content compared to females lactating in a year of high forage production. Females nursing in late winter produced milk with more lipids compared to females at the same stage of lactation in late spring, whose milk had a higher proportion of protein. The milk of larger females contained more protein than lipid, and females in better condition allocated higher proportions of protein to sons than to daughters. Increased protein concentration in milk was correlated with offspring longevity, and this effect was stronger for sons than daughters. A seasonally modulated lactation strategy enables the adjustment of milk composition to available resources. Condition‐specific protein allocation in favor of sons for mothers of higher caring ability suggests adaptive sex‐biased maternal care in this highly sexually dimorphic mammal.

A comprehensive test of the Trivers–Willard hypothesis in pronghorn ( Antilocapra americana )

Abstract The Trivers–Willard hypothesis (TWH) predicts that in a polygynous mating system, when fitness of male offspring is more variable than fitness of female offspring, mothers should invest more heavily in the sex with the highest marginal fitness returns. Females in good condition or high social rank should benefit by investing in sons, and females in poor condition or low social rank should benefit by investing in daughters. Many empirical studies have tested different aspects of the TWH, but no study has tested the assumptions and predictions in a single polygynous species using measures of maternal condition and maternal social rank, while accounting for random effects that can also influence offspring growth and survival. Here, we followed individuals in an isolated population of pronghorn on the National Bison Range, Montana, over multiple generations and tested the assumptions and predictions of the TWH. Pronghorn females who were in good condition or were socially dominant weaned larger fawns that were in better condition, but this advantage did not increase male fawn survival or reproductive success. We detected a slight bias in birth sex ratios according to maternal social rank, but overall we did not detect any adaptive benefit to mothers adopting a sex-biased investment strategy.

High density, maternal condition, and stress are associated with male-biased sex allocation in a marsupial

Many mammals have been reported to significantly bias their offspring sex ratios, but these deviations from equality have been difficult to understand and are often inconsistent even within the same species. Evolutionary theory predicts a number of scenarios where females should bias their investment to one sex over the other; when fitness returns are sex specific, selection favors the facultative adjustment of offspring sex ratios to the sex with the highest inclusive fitness return. Interpreting sex allocation in mammals within the framework of classic sex allocation theory is challenging given the complex life histories and social interactions of species, hence it is likely that there are multiple mechanisms and selective forces dependent upon maternal and environmental drivers. Here, we show the previously demonstrated condition-dependent sex allocation in bridled nailtail wallabies (Onychogalea fraenata), where females in better condition were more likely to have sons, was reversed under high population densities and elevated maternal stress. In this solitary species, an elevated glucocorticoid stress response under unnaturally high densities likely influences adaptive sex allocation to the dispersive sex, consistent with the local resource competition theory. Managing factors such as population density, maternal stress, and food resources may be used to adjust offspring sex ratios in this endangered species.

Sexual signals for the colour‐blind: cryptic female mantids signal quality through brightness

Summary Cryptic coloration may evolve in response to selective pressure imposed by predators, yet effective intraspecific communication may require some level of detectability. This creates a tension between the benefits of sexually selected visual traits and the predatory costs imposed by greater conspicuousness, and little is known about how this tension may be ameliorated in highly cryptic species. We explore these competing demands in the false garden mantid Pseudomantis albofimbriata, a colour‐blind and seemingly cryptic insect. We use reflectance spectrometry and receptor‐noise modelling to characterize the conspicuousness of mantid body regions in the visual systems of mates (mantids), as well as potential predators (birds) and prey (bees). We then use condition manipulation and conspecific choice tests to further explore the colour traits of interest. Based on visual modelling, we find that male mantids are inconspicuous to conspecifics, prey and predators – that is, they are chromatically and achromatically cryptic. In contrast, female mantids are chromatically cryptic to all potential receivers, but their abdomens are achromatically conspicuous. Our food manipulation experiment shows that females in good condition (and therefore with more eggs) have brighter abdomens than females in poor condition. Choice assays show male mantids are consistently attracted to females bearing brighter abdomens. Our results reveal brightness‐mediated sexual signalling in a colour‐blind and classically cryptic insect. By communicating in the only visual channel available to them, female mantids are conspicuously signalling their quality to mates, while potentially minimizing their conspicuousness to predators and prey. Furthermore, by signalling with only a single body region, female mantids are apparently using coincident disruptive coloration to further decrease detectability to potential eavesdroppers. Our data reveal a novel example of the way in which the trade‐off between sexual selection for conspicuousness and natural selection for crypsis may be mediated in a visual signalling system. Such signals may be common in apparently cryptic species, and this study once again demonstrates the importance of analysing visual signals beyond the capacity of human vision.

Reproductive life-history strategies in lake whitefish (Coregonus clupeaformis) from the Laurentian Great Lakes

Recent food-web changes in the Laurentian Great Lakes are affecting energy and nutrient allocation to lake whitefish (Coregonus clupeaformis) with potential downstream effects on egg condition and recruitment. We tested whether egg condition was conserved or varied with maternal condition in eight stocks from Lakes Erie, Michigan, and Superior. Egg condition was conserved across stocks based on (i) a lack of correlation between females and eggs for total lipid, DHA, and other essential fatty acids; (ii) higher levels of energy and long-chain polyunsaturated fatty acids (LC-PUFA) in eggs compared with females; and (iii) no among-stock differences for those same variables in eggs. Females from northern Lake Michigan generally made the greatest trade-offs between egg size and fecundity. Highly fecund females provisioned less lipid, but more n-3 LC-PUFA to their eggs. A lack of stock-level patterns in energy and nutrient allocation suggests that trade-offs occur at the level of individual females and that females in poor condition make greater trade-offs among egg size and fecundity, total lipids, and n-3 LC-PUFA than females in good condition.