Why do males emerge before females? protandry as a mating strategy in male and female butterflies

Summary The reproductive strategy of butterfly males can be defined as being to maximize the number of females mated. We have earlier shown that, if the eclosion period of females is regarded as given, males should emerge before females to achieve maximal reproductive success. However, females may also be considered to have a reproductive strategy with respect to the issue when to emerge. In this paper we assume that females are selected to minimize the time spent unmated (to minimize prereproductive death), and analyze when females should optimally emerge in relation to males to achieve this end. We show that there is no conflict between the sexes with respect to the timing of eclosion when the length of the eclosion period is approximately equal for males and females. Thus, protandry should be considered a reproductive strategy of both males and females.     

Variable male potential rate of reproduction: high male mating capacity as an adaptation to parasite-induced excess of females?

Numerous animals are known to harbour intracytoplasmic symbionts that gain transmission to a new host generation via female eggs and not male sperm. Bacteria of the genus Wolbachia are a typical example. They infect a large range of arthropod species and manipulate host reproduction in several ways. In terrestrial isopods (woodlice), Wolbachia are responsible for converting males into females (feminization (F)) in some species, or for infertility in certain host crosses in other species (cytoplasmic incompatibility (CI)). Wolbachia with the F phenotype impose a strong excess of females on their host populations, while Wolbachia expressing CI do not. Here, we test the possibility that male mating capacity (MC) is correlated with Wolbachia-induced phenotype. We show that males of isopod hosts harbouring F Wolbachia possess a strong MC (i.e. are able to mate with several females in a short time), while those of species harbouring CI Wolbachia possess a weaker MC. This pattern may be explained either by the selection of high MC following the increase in female-biased sex ratios, or because the F phenotype would lead to population extinction in species where MC is not sufficiently high. This last hypotheses is nevertheless more constrained by population structure.     

Egg size in relation to body size in rotifers: an indication of reproductive strategy?

Egg sizes and body sizes of 43 egg-bearing rotifer species of numerous, mostly tropical, general have been recorded. Larger absolute egg volumes have been found for larger rotifer species, but the increase was lower than expected in proportion to body size, i.e. the relative egg volume decreased with increasing body size. Obviously the relative investment per offspring is smaller in larger rotifer species.     

The causes of physiological suppression among female meerkats: a role for subordinate restraint due to the threat of infanticide?

In many animal societies, subordinates exhibit down-regulated reproductive endocrine axes relative to those of dominants, but whether this 'physiological suppression' arises from active interference by dominants or subordinate self-restraint is a matter of debate. Here we investigate the roles that these processes play in precipitating physiological suppression among subordinate female meerkats, Suricata suricatta. We show that, while subordinate females are known to suffer stress-related physiological suppression during periodic temporary evictions by the dominant female, their low estrogen levels while within their groups cannot be readily attributed to chronic stress, as their fecal glucocorticoid metabolite levels during this time are comparable to those of dominants. The low estrogen levels of subordinate females also cannot be explained simply by self-restraint due to factors that could reduce their payoff from maintaining their fertility regardless of the presence of the dominant female (young age, a lack of unrelated mates, poor body condition and limited breeding experience), as substantial rank-related differences in fecal total-estrogen metabolite levels remain when such factors are controlled. We suggest that this residual difference in estrogen levels may reflect a degree of subordinate restraint due in part to the dominant female's ability to kill their young. Accordingly, subordinate female estrogen levels vary in association with temporal variation in the likelihood of infanticide by the dominant. Attempts to identify the causes of physiological suppression should be cautious if rejecting any role for dominant interference in favor of subordinate restraint, as the dominant's capacity to interfere may often be the reason why subordinates exercise restraint.     

Maternal modulation of natal dispersal in a passerine bird: an adaptive strategy to cope with parasitism?

The decision of how far to disperse from the natal territory has profound and long-lasting consequences for young animals, yet the optimal dispersal behavior often depends on environmental factors that are difficult or impossible to assess by inexperienced juveniles. Natural selection thus favors mechanisms that allow the adaptive and flexible adjustment of the offspring's dispersal behavior by their parents via either paternal or maternal effects. Here we show that different dispersal strategies maximize the reproductive success of young great tits (Parus major) originating from a parasite-infested or a parasite-free nest and demonstrate that differential transfer of maternal yolk androgens in response to parasitism can result in a modification of the offspring's dispersal behavior that appears adaptive. It demonstrates that prenatal maternal effects are an important yet so far neglected determinant of natal dispersal and highlights the potential importance of maternal effects in mediating coevolutionary processes in host-parasite systems.     

Are female reproductive status and male morphotypes of the giant freshwater prawn Macrobrachium rosenbergii altered by selection for high growth?

Understanding genetic changes in the hierarchical population structure of the giant freshwater prawn (GFP) Macrobrachium rosenbergii is important to improve productivity and profitability of prawn farming. We examined correlated responses in male morphotype and female reproduction status resulting from a selection programme for high growth in a GFP population undergoing four generations of selection. Two contemporary lines (selection and control) were maintained and produced simultaneously; the selection line was selected for high breeding values for harvest body weight and the control for average breeding values of the population. A total of 21,459 individual prawns were measured for body traits and morphotypes. Individual morphotype was recorded as a binary trait (0 and 1) and were analysed using a generalised threshold mixed model with a logit link function. Correlated genetic changes in three important male morphotypes (small, orange and blue claw males) were significant (p < 0.05–0.001) only in generation 2010 but not in the last generation (2012). Selection for high growth did not have an adverse effect on reproduction status of females, except that the selection line had a greater proportion of spawned females than the control (p = 0.01). Our results pointed out that selection for high growth may have had both positive and negative impacts on the social population structure of male morphotypes in GFP. Undesired changes in important morphotypes should be taken account of in genetic improvement programmes for GFP in order to minimise social competition effects and increase total biomass and consequently economic returns of the sector.     

Ranging behaviour of roe deer in an experimental high-density population: Are females territorial?

We studied the ranging behaviour and spatial relationships between seven roe deer during more than 4 years in a partly wooded 14.2-ha enclosure. The animals (three young males, four adult females) were monitored with GPS telemetry collars. As expected, the surface area and overlap of the males’ bimonthly ranges decreased, and the distance between their arithmetic centres increased, as they became adult and, for two of them, territorial. Unexpectedly, females also tended to space out, the surface area and overlap of their bimonthly ranges being minimal in May to June, i.e. during the birth period. The distance between their arithmetic centres reached its maximum at the same time. Overlap between females’ ranges was consistently lower than those between males and females’ ranges, or between 1-year old males’ ranges. Our results raise the questions of female seasonal territoriality and of independence of the spacing systems of the two sexes in roe deer.     

When and where to count? Implications of migratory connectivity and nonbreeding distribution to population censuses in a migratory bird population

Migratory connectivity is a metric of the co-occurrence of migratory animals originating from different breeding sites, and like their spatial dispersion, can vary substantially during the annual cycle. Together, both these properties affect the optimal times and sites of population censusing. We tracked taiga bean geese (Anser fabalis fabalis) during 2014–2021 to study their migratory connectivity and nonbreeding movements and determine optimal periods to assess the size of their main flyway population. We also compared available census data with tracking data, to examine how well two existing censuses covered the population. Daily Mantel's correlation between breeding and nonbreeding sites lay between 0 and 0.5 during most of the nonbreeding season, implying birds from different breeding areas were not strongly separated at other times in the annual cycle. However, the connectivity was higher among birds from the westernmost breeding areas compared to the birds breeding elsewhere. Daily Minimum Convex Polygons showed tracked birds were highly aggregated at census times, confirming their utility. The number of tracked birds absent at count sites during the censuses however exceeded numbers double-counted at several sites, indicating that censuses might have underestimated the true population size. Our results show that connectivity can vary in different times during the nonbreeding period, and should be studied throughout the annual cycle. Our results also confirm previous studies, which have found that estimates using marked individuals usually produce higher population size estimates than total counts. This should be considered when using total counts to assess population sizes in the future.     

The case of an infertile male with an uncommon reciprocal X-autosomal translocation: how does this affect male fertility?

Infertility is defined as the inability to conceive after one year of regular unprotected intercourse. Constitutional numerical and/or structural chromosomal aberrations like sex-chromosome aberrations are one of the possible factors involved in fertility problems. Reciprocal translocations between an X-chromosome and an autosome are rarely seen in men. Male carriers of an X-autosome translocation are invariably sterile, regardless of the position of the breakpoint in the X-chromosome. Breakpoints in autosomal chromosomes could also be involved in male infertility. In this paper, we describe a 31-year-old male with azoospermia. GTG banding with high resolution multicolor-banding (MCB) techniques revealed a karyotype 46,Y,t(X;1)(p22.3;q25), and we discuss how the breakpoint of this translocation could affect male infertility. As a conclusion, cytogenetic evaluation of infertile subjects with azoospermia should be considered in the first place before in vitro fertilisation procedures are planned.     

Yolk androgen deposition without an energetic cost for female rockhopper penguins: a compensatory strategy to accelerate brood reduction?

Whether androgen deposition in eggs is physiologically costly for female birds has remained a crucial but unsolved question, despite a broad use of this assumption in functional studies. We tested whether females depositing high androgen concentrations experienced higher mass losses than females depositing low androgen concentrations. Analysing female body mass change during egg formation in rockhopper penguins (Eudyptes chrysocome chrysocome), we observed no energetic cost to androgen deposition. Nevertheless, lighter females laid eggs with higher yolk androgen concentrations. This relationship existed only for the second-laid egg (B-egg), but not for the first-laid egg (A-egg). Since the B-egg is usually the first to hatch and the only one to produce a fledging chick, we hypothesize that differential yolk androgen deposition may be an adaptive strategy for females to affect brood reduction.     

Transgenerational consequences of plant responses to herbivory: an adaptive maternal effect?

Herbivory has many effects on plants, ranging from shifts in primary processes such as photosynthesis, growth, and phenology to effects on defense against subsequent herbivores and other species interactions. In this study, I investigated the effects of herbivory on seed and seedling characteristics of several families of wild radish (Raphanus raphanistrum) to test the hypothesis that herbivory may affect the quality of offspring and the resistance of offspring to plant parasites. Transgenerational effects of herbivory may represent adaptive maternal effects or factors that constrain or amplify natural selection on progeny. Caterpillar (Pieris rapae) herbivory to greenhouse-grown plants caused plants in some families to produce smaller seeds and those in other families to produce larger seeds compared with undamaged controls. Seed mass was positively associated with probability of emergence in the field. The number of setose trichomes, a putative plant defense, was higher in the progeny of damaged plants in some families and lower in the progeny of damaged plants in other families. In a field experiment, plant families varied in their resistance to several herbivores and pathogens as well as in growth rate and time to flowering. Seeds from damaged parent plants were more likely to become infested with a plant virus. Although herbivory on maternal plants did not directly affect interactions of offspring with other plant parasites, seed mass influenced plant resistance to several attackers. Thus, herbivory affected seed characters, which mediated interactions between plants and their parasites. Finally, irrespective of seed mass, herbivory on maternal plants influenced components of progeny fitness, which was dependent on plant family. Natural selection may act on plant responses to herbivory that affect seedling-parasite interactions and, ultimately, fitness.     

Behavioural and life‐history regulation in a unisexual/bisexual mating system: does male mate choice affect female reproductive life histories?

In theory, unisexual taxa have an advantage over ecologically similar bisexual species because unisexuals produce twice as many daughters and, thus, should quickly outcompete coexisting bisexuals in any given population. For sperm‐dependent unisexual (gynogenetic) species, stable coexistence with their bisexual sperm donors can be postulated if male mate choice puts unisexual females at a disadvantage through sperm limitation, thus halving their reproductive output compared to bisexuals (‘behavioural regulation hypothesis’). We tested for a potential life‐history signature of male mate choice in a system of coexisting bisexual sailfin mollies (Poecilia latipinna) and gynogenetic Amazon mollies (Poecilia formosa). Specifically, we gave P. latipinna males an opportunity to freely interact (and mate) with both types of females and, after 25 days, quantified the proportion of (1) females with sperm in their genital tract and (2) pregnant females. A higher proportion of P. latipinna females (53.7%) had sperm in their genital tract (compared to only 25.9% in P. formosa), corroborating a previous study on wild‐caught fish. This translated into a higher frequency (42.6%) of P. latipinna females being pregnant (compared to 29.6% in P. formosa); however, among pregnant females, no significant differences between species in reproductive life‐history traits (such as offspring number or size) were uncovered. Hence, although the findings of the present study confirm that male discrimination against unisexual females leads to reduced reproductive output in unisexuals, the observed magnitude of differences in targeted life histories between the two types of females is unlikely to be the sole factor regulating stable coexistence in this system. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 106 , 598–606.     

Thermoregulatory responses to variations of photoperiod and ambient temperature in the male lesser mouse lemur: a primitive or an advanced adaptive character?

The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in ambient temperature, evaporative water loss (EWL), body temperature (T _b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions. In both photoperiods, EWL, T _b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated with a decrease in T _b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T _b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed according to daylength. Daily variations in T _b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T _b decrease with or without the occurrence of torpor (T _b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations. Accepted: 4 August 1998     

Scattered trees: a complementary strategy for facilitating adaptive responses to climate change in modified landscapes?

1.  Facilitating adaptive responses of organisms in modified landscape will be essential to overcome the negative effects of climate change and its interaction with land use change. Without such action, many organisms will be prevented from achieving the predicted range shifts they need to survive.
2.  Scattered trees are a prominent feature of many modified landscapes, and could play an important role in facilitating climate change adaptation. They are keystone structures because of the disproportionally large ecological values and ecosystem services that they provide relative to the area they occupy in these landscapes. The provision of habitat and connectivity will be particularly relevant.
3.  Scattered trees are declining in modified landscapes due to elevated tree mortality and poor recruitment often associated with intensive land use. The continuing global decline of scattered trees will undermine the capacity of many organisms to adapt to climate change.
4.   Synthesis and applications. The sustainable management of scattered trees in modified landscapes could complement other strategies for facilitating climate change adaptation. They create continuous, though sparse, vegetation cover that permits multi-directional movements of biota across landscapes and ecological networks. They have the capacity to span ecosystems and climatic gradients that cannot be captured in formal reserves alone. The management of scattered trees should be an integral part of conservation objectives and agricultural activities in modified landscapes. Public investment, through mechanisms such as agri-environmental schemes, in rotational grazing, temporary set-asides, tree-planting and regulations that reduce clearing and early mortality among standing trees will improve the capacity of biota to adapt to climate change.     

Voltage-activated current properties of male and female mouse vomeronasal sensory neurons: sexually dichotomous?

The vomeronasal organ, the chemosensory organ of the vomeronasal system, is vital in determining sexual and gender-specific behavior in mice. Here, whole-cell voltage-activated currents of individual mouse vomeronasal sensory neurons of two strains (BALB/c and CBA) were measured and correlated to sex in each strain. The average resting membrane potentials, maximal outward current magnitudes, and kinetics of activation and inactivation, were found to be independent of sex. Maximal inward current magnitudes differed significantly across gender in CBA, whereas they did not significantly differ in male and female BALB/c mice: BALB/c males –347±45 pA (n=51), and females –430±56 pA (n=27); CBA males –308±36 pA (n=56) and females –155±18 pA (n=28). These results suggest that some voltage-activated properties may differ slightly according to gender and to strain.D.M. Dean and A. Mazzatenta contributed equally to this work     

Do males choose their mates in the lekking moth Achroia grisella? Influence of female body mass and male reproductive status on male mate choice

Lekking males aggregate to attract females and contribute solely to egg fertilization, without any further parental care. Evolutionary theory therefore predicts them to be nonchoosy toward their mates, because any lost mating opportunities would outweigh the benefits associated with such preferences. Nevertheless, due to time costs, the production of energetically costly sexual displays, and potential sperm limitation, the mating effort of lekking males is often considerable. These factors, combined with the fact that many females of varying quality are likely to visit leks, could favor the evolution of male mate preferences. Here, we show that males of the lekking lesser wax moth, Achroia grisella, were indeed more likely to mate with heavier females in choice experiments, even at their virgin mating (i.e., when their reproductive resources have not yet been depleted by previous matings). This differential female mating success could not be attributed to female behavior as heavy and light females showed similar motivation to mate (i.e., latency to approach the males) and time to copulate. Males seem to benefit from mating with heavier females, as fecundity positively correlated with female mass. This new empirical evidence shows that male mate choice may have been underestimated in lekking species.     

Diet and reproductive success of Adélie and chinstrap penguins: linking response of predators to prey population dynamics

The diet and reproductive performance of two sympatric penguin species were studied at Signy Island, South Orkney Islands between 1997 and 2001. Each year, Adélie (Pygoscelis adeliae) and chinstrap (P. antarctica) penguins fed almost exclusively (>99% by mass) on Antarctic krill; however, there was considerable inter-annual variation in reproductive output. In 1998, chinstrap penguins were adversely affected by extensive sea-ice in the vicinity of the colony, whereas Adélie penguins were unaffected by this. However, in 2000, both species suffered reduced reproductive output. Detailed analysis of the population-size structure of krill in the diet indicated a lack of recruitment of small krill into the population since 1996. A simple model of krill growth and mortality indicated that the biomass represented by the last recruiting cohort would decline dramatically between 1999 and 2000. Thus, despite the lack of a change in the proportion of krill in the diet, the population demographics of the krill population suggested that the abundance of krill may have fallen below the level required to support normal breeding success of penguins sometime before or during the 2000 breeding season. The role of marine predators as indicator species is greatly enhanced when studies provide data reflecting not only the consequences of changes in the ecosystem but also those data that elucidate the causes of such changes.     

The relationship between female brooding and male nestling provisioning: does climate underlie geographic variation in sex roles?

Comparative studies of populations occupying different environments can provide insights into the ecological conditions affecting differences in parental strategies, including the relative contributions of males and females. Male and female parental strategies reflect the interplay between ecological conditions, the contributions of the social mate, and the needs of offspring. Climate is expected to underlie geographic variation in incubation and brooding behavior, and can thereby affect both the absolute and relative contributions of each sex to other aspects of parental care such as offspring provisioning. However, geographic variation in brooding behavior has received much less attention than variation in incubation attentiveness or provisioning rates. We compared parental behavior during the nestling period in populations of orange‐crowned warblers Oreothlypis celata near the northern (64°N) and southern (33°N) boundaries of the breeding range. In Alaska, we found that males were responsible for the majority of food delivery whereas the sexes contributed equally to provisioning in California. Higher male provisioning in Alaska appeared to facilitate a higher proportion of time females spent brooding the nestlings. Surprisingly, differences in brooding between populations could not be explained by variation in ambient temperature, which was similar between populations during the nestling period. While these results represent a single population contrast, they suggest additional hypotheses for the ecological correlates and evolutionary drivers of geographic variation in brooding behavior, and the factors that shape the contributions of each sex.