Life history of the Glanville fritillary butterfly in fragmented versus continuous landscapes

Habitat loss and fragmentation threaten the long‐term viability of innumerable species of plants and animals. At the same time, habitat fragmentation may impose strong natural selection and lead to evolution of life histories with possible consequences for demographic dynamics. The Baltic populations of the Glanville fritillary butterfly (Melitaea cinxia) inhabit regions with highly fragmented habitat (networks of small dry meadows) as well as regions with extensive continuous habitat (calcareous alvar grasslands). Here, we report the results of common garden studies on butterflies originating from two highly fragmented landscapes (FL) in Finland and Sweden and from two continuous landscapes (CL) in Sweden and Estonia, conducted in a large outdoor cage (32 by 26 m) and in the laboratory. We investigated a comprehensive set of 51 life‐history traits, including measures of larval growth and development, flight performance, and adult reproductive behavior. Seventeen of the 51 traits showed a significant difference between fragmented versus CL. Most notably, the growth rate of postdiapause larvae and several measures of flight capacity, including flight metabolic rate, were higher in butterflies from fragmented than CL. Females from CL had shorter intervals between consecutive egg clutches and somewhat higher life‐time egg production, but shorter longevity, than females from FL. These results are likely to reflect the constant opportunities for oviposition in females living in continuous habitats, while the more dispersive females from FL allocate more resources to dispersal capacity at the cost of egg maturation rate. This study supports theoretical predictions about small population sizes and high rate of population turnover in fragmented habitats selecting for increased rate of dispersal, but the results also indicate that many other life‐history traits apart from dispersal are affected by the degree of habitat fragmentation.     

The effect of different chiral morphs on visitation rates and fruit set in the orchid Spiranthes spiralis

Background: The arrangement of flowers on inflorescences is important for determining the movement of pollinators within the inflorescence and, consequently, the overall mating success and fruit set of a plant.

Aims: Spiranthes spiralis is an orchid that has a spiralled inflorescence. The species has two chiral forms that show opposite coiling directions (clockwise and anti-clockwise). We tested if this arrangement of inflorescence influences pollinator attraction and behaviour.

Methods: We surveyed two natural populations, analysed the reproductive compatibility of the two morphs and estimated pollination success in natural and experimental populations.

Results: We found that the two morphs were not isolated by pre- or post-mating barriers, occurred with a similar proportion in natural populations and showed similar levels of pollination success both in natural and artificial populations. However, we found a different pattern of pollination success along the inflorescences. In the two morphs, lower flowers experienced a higher pollination rate and this rate decreased along the inflorescence faster in anti-clockwise than in clockwise individuals.

Conclusions: This finding suggests that pollinators visit the flowers sequentially from the lower part of the inflorescences and leave the anti-clockwise individuals more rapidly than the clockwise ones. However, this pollinator behaviour is not detrimental for the pollination success of either of the two morphs.     

Provisioning habitat with custom‐designed nest‐boxes increases reproductive success in an endangered finch

Manipulating resource availability to assess the strength and effects of resource limitation on an animal population is relatively straightforward, and thus, common in the scientific literature. Resource quality, however, is rarely manipulated, as this requires a priori knowledge of a relationship between some measurable variation in the resource and individual preference and/or fitness. Recent research on nest‐site selection was used to inform the design of custom‐built nest‐boxes for an endangered hollow‐nester, the Gouldian finch (Erythrura gouldiae). By provisioning breeding populations with these ‘high quality’ artificial nest sites over 3 years, we experimentally investigated the strength and effects of nest‐site limitation in this species. Breeding pairs using nest‐boxes initiated nesting earlier, produced larger clutches and fledged more offspring per season than those in natural hollows. Total and mean reproductive output also increased in nest‐box provisioned sites over the duration of the study. All of these effects were predominantly driven by pairs initiating clutches earlier, potentially because of the reduced intra‐ and interspecific competition for nest sites at optimal breeding times. Our findings suggest that reproduction in wild Gouldian finch populations may be limited by the availability of high quality nest sites in the landscape, and that nest‐boxes could be used as a tool for enhancing reproduction in recovering populations. Furthermore, we conclude that resource quality is equally, if not more important than quantity when supplementing resource‐limited habitats.     

The short‐ and long‐term fitness consequences of natal dispersal in a wild bird population

Dispersal is a key process in population and evolutionary ecology. Individual decisions are affected by fitness consequences of dispersal, but these are difficult to measure in wild populations. A long‐term dataset on a geographically closed bird population, the Mauritius kestrel, offers a rare opportunity to explore fitness consequences. Females dispersed further when the availability of local breeding sites was limited, whereas male dispersal correlated with phenotypic traits. Female but not male fitness was lower when they dispersed longer distances compared to settling close to home. These results suggest a cost of dispersal in females. We found evidence of both short‐ and long‐term fitness consequences of natal dispersal in females, including reduced fecundity in early life and more rapid aging in later life. Taken together, our results indicate that dispersal in early life might shape life history strategies in wild populations.     

Intergenerational effects of inbreeding in Nicrophorus vespilloides: offspring suffer fitness costs when either they or their parents are inbred

Inbreeding depression is the reduction in fitness caused by mating between related individuals. Inbreeding is expected to cause a reduction in offspring fitness when the offspring themselves are inbred, but outbred individuals may also suffer a reduction in fitness when they depend on care from inbred parents. At present, little is known about the significance of such intergenerational effects of inbreeding. Here, we report two experiments on the burying beetle Nicrophorus vespilloides, an insect with elaborate parental care, in which we investigated inbreeding depression in offspring when either the offspring themselves or their parents were inbred. We found substantial inbreeding depression when offspring were inbred, including reductions in hatching success of inbred eggs and survival of inbred offspring. We also found substantial inbreeding depression when parents were inbred, including reductions in hatching success of eggs produced by inbred parents and survival of outbred offspring that received care from inbred parents. Our results suggest that intergenerational effects of inbreeding can have substantial fitness costs to offspring, and that future studies need to incorporate such costs to obtain accurate estimates of inbreeding depression.     

Heterospecific courtship,minority effects and niche separation between cryptic butterfly species

Species interacting in varied ecological conditions often evolve in different directions in different local populations. The butterflies of the cryptic Leptidea complex are sympatrically distributed in different combinations across their Eurasian range. Interestingly, the same species is a habitat generalist in some regions and a habitat specialist in others, where a sibling species has the habitat generalist role. Previous studies suggest that this geographically variable niche divergence is generated by local processes in different contact zones. By varying the absolute and relative densities of Leptidea sinapis and Leptidea juvernica in large outdoor cages, we show that female mating success is unaffected by conspecific density, but strongly negatively affected by the density of the other species. Whereas 80% of the females mated when a conspecific couple was alone in a cage, less than 10% mated when the single couple shared the cage with five pairs of the other species. The heterospecific courtships can thus affect the population fitness, and for the species in the local minority, the suitability of a habitat is likely to depend on the presence or absence of the locally interacting species. If the local relative abundance of the different species depends on the colonization order, priority effects might determine the ecological roles of interacting species in this system.     

Stochastic exits from dormancy give rise to heavy‐tailed distributions of descendants in bacterial populations

Variance in reproductive success is a major determinant of the degree of genetic drift in a population. While many plants and animals exhibit high variance in their number of progeny, far less is known about these distributions for microorganisms. Here, we used a strain barcoding approach to quantify variability in offspring number among replicate bacterial populations and developed a Bayesian method to infer the distribution of descendants from this variability. We applied our approach to measure the offspring distributions for five strains of bacteria from the genus Streptomyces after germination and growth in a homogenous laboratory environment. The distributions of descendants were heavy‐tailed, with a few cells effectively ‘winning the jackpot’ to become a disproportionately large fraction of the population. This extreme variability in reproductive success largely traced back to initial populations of spores stochastically exiting dormancy, which provided early‐germinating spores with an exponential advantage. In simulations with multiple dormancy cycles, heavy‐tailed distributions of descendants decreased the effective population size by many orders of magnitude and led to allele dynamics differing substantially from classical population genetics models with matching effective population size. Collectively, these results demonstrate that extreme variability in reproductive success can occur even in growth conditions that are far more homogeneous than the natural environment. Thus, extreme variability in reproductive success might be an important factor shaping microbial population dynamics with implications for predicting the fate of beneficial mutations, interpreting sequence variability within populations and explaining variability in infection outcomes across patients.     

Close‐kin mating,but not inbred parents,reduces hatching rates and offspring quality in a threatened tortoise

Inbreeding depression, the reduction in fitness due to mating of related individuals, is of particular conservation concern in species with small, isolated populations. Although inbreeding depression is widespread in natural populations, long‐lived species may be buffered from its effects during population declines due to long generation times and thus are less likely to have evolved mechanisms of inbreeding avoidance than species with shorter generation times. However, empirical evidence of the consequences of inbreeding in threatened, long‐lived species is limited. In this study, we leverage a well‐studied population of gopher tortoises, Gopherus polyphemus, to examine the role of inbreeding depression and the potential for behavioural inbreeding avoidance in a natural population of a long‐lived species. We tested the hypothesis that increased parental inbreeding leads to reduced hatching rates and offspring quality. Additionally, we tested for evidence of inbreeding avoidance. We found that high parental relatedness results in offspring with lower quality and that high parental relatedness is correlated with reduced hatching success. However, we found that hatching success and offspring quality increase with maternal inbreeding, likely due to highly inbred females mating with more distantly related males. We did not find evidence for inbreeding avoidance in males and outbred females, suggesting sex‐specific evolutionary trade‐offs may have driven the evolution of mating behaviour. Our results demonstrate inbreeding depression in a long‐lived species and that the evolution of inbreeding avoidance is shaped by multiple selective forces.     

Field estimates of fitness costs of the pace‐of‐life in an endangered damselfly

Theory predicts that within‐population differences in the pace‐of‐life can lead to cohort splitting and produce marked intraspecific variation in body size. Although many studies showed that body size is positively correlated with fitness, many argue that selection for the larger body is counterbalanced by opposing physiological and ecological selective mechanisms that favour smaller body. When a population split into cohorts with different paces of life (slow or fast cohort), one would expect to detect the fitness–size relationship among and within cohorts, that is, (a) slower‐developing cohort has larger body size and higher fitness than faster‐developing cohort, and (b) larger individuals within each cohort show higher fitness than smaller individuals. Here, we test these hypotheses in capture–mark–recapture field surveys that assess body size, lifespan, survival and lifetime mating success in two consecutive generations of a partially bivoltine aquatic insect, Coenagrion mercuriale, where the spring cohort is slower‐developing than the autumn cohort. As expected, body size was larger in the slow‐developing cohort, which is consistent with the temperature‐size rule and also with the duration of development. Body size seasonal variation was greater in slow‐developing cohort most likely because of the higher variation in age at maturity. Concordant with theory, survival probability, lifespan and lifetime mating success were higher in the slow‐developing cohort. Moreover, individual body size was positively correlated with survival and mating success in both cohorts. Our study confirms the fitness costs of fast pace‐of‐life and the benefits of larger body size to adult fitness.     

Spatially balanced sampling and ground‐level imagery for vegetation monitoring on reclaimed well pads

Land reclamation associated with natural gas development has become increasingly important to mitigate land surface disturbance in western North America. Since well pads occur on sites with multiple land use and ownership, the progress and outcomes of these efforts are of interest to multiple stakeholders including industry, practitioners and consultants, regulatory agents, private landowners, and the scientific community. Reclamation success criteria often vary within, and among, government agencies and across land ownership type. Typically, reclamation success of a well pad is judged by comparing vegetation cover from a single transect on the pad to a single transect in an adjacent reference site and data are collected by a large number of technicians with various field monitoring skills. We utilized “SamplePoint” image analysis software and a spatially balanced sampling design, called balanced acceptance sampling, to demonstrate how spatially explicit quantitative data can be used to determine if sites are meeting various reclamation success criteria and used chi‐square tests to show how sites in vegetation percent cover differ from a statistical standpoint. This method collects field data faster than traditional methods. We demonstrate how quantitative and spatially explicit data can be utilized by multiple stakeholders, how it can improve upon current reference site selection, how it can satisfy reclamation monitoring requirements for multiple regulatory agencies, how it may help improve future seed mix selection, and discuss how it may reduce costs for operations responsible for reclamation and how it may reduce observer bias.