Dispersal Propensity Research Articles

Habitat Association Predicts Population Connectivity and Persistence in Flightless Beetles: A Population Genomics Approach Within a Dynamic Archipelago.

Habitat association has been proposed to affect evolutionary dynamics through its control on dispersal propensity, which is considered a key trait for lineage survival in habitats of low durational stability. The Habitat Constraint hypothesis predicts different micro- and macroevolutionary patterns for stable versus dynamic habitat specialists, but the empirical evidence remains controversial and in insects mostly derives from winged lineages. We here use genome-wide SNP data to assess the effect of habitat association on the population dynamics of two closely related flightless lineages of the genus Eutagenia (Coleoptera: Tenebrionidae), which are co-distributed across the Cyclades islands in the Eastern Mediterranean but are associated with habitat types of different presumed stability: the psammophilous lineage is associated with dynamic sandy coastal habitats, while the geophilous lineage is associated with comparatively stable compact soil habitats. Our comparative population genomic and demographic analyses support higher inter-island gene flow in the psammophilous lineage, presumably due to the physical properties of dynamic sand-dune habitats that promote passive dispersal. We also find consistent bottlenecks in the psammophilous demes, suggesting that lineage evolution in the dynamic habitat is punctuated by local extinction and recolonisation events. The inferred demographic processes are surprisingly uniform among psammophilous demes, but vary considerably among geophilous demes depending on historical island connectivity, indicating more stringent constraints on the dynamic habitat lineage. This study extends the Habitat Constraint hypothesis by demonstrating that selection on dispersal traits is not the only mechanism that can drive consistent differences in evolutionary dynamics between stable versus dynamic habitat specialists.

Dispersal and gene flow in anadromous salmonids: A systematic review

AbstractDispersal is a ubiquitous ecological process that has been extensively studied in many plants and animals. Anadromous salmonids are an interesting system for examining dispersal, in part because of their well‐known philopatric behaviour, but also because of the conservation challenges related to the dispersal of hatchery‐origin fish. Building on earlier work, we provide an updated systematic review of dispersal and gene flow in anadromous salmonids. In particular, we compared studies on the dispersal of anadromous salmonids from wild and hatchery origins, including studies providing estimates of dispersal rates, observations of dispersal and results from modelling studies. We reviewed 228 studies and found these were unevenly distributed among species, with Atlantic salmon, Chinook salmon and sea trout being well‐represented. Our results showcase considerable variability in estimated dispersal rates within and across studies, which is likely related to the different methodologies, dispersal propensities across species and populations, and spatial extents considered. Overall, our results confirmed a higher tendency of hatchery fish to disperse relative to wild fish, but we also found some variation across species that warrants further study. Moreover, we found that dispersal propensity tended to decline exponentially with distance and that the drivers of dispersal varied considerably among studies. Additionally, we highlight various facets of dispersal captured across this suite of studies, including variation in terminology, methods and metrics for characterising dispersal, and the spatio‐temporal scales considered. Finally, our review revealed that few studies considered, and even fewer assessed, the implications of dispersal for the conservation and management of anadromous salmonids.

Landscape effects on dispersal‐related traits in a sedentary butterfly in agricultural landscapes

Abstract Agricultural intensification causes the loss and fragmentation of natural habitats, which negatively impacts farmland biodiversity. The concomitant isolation of essential resources may favour increased dispersal ability in flying insects, resulting in differences in flight morphology and dispersal propensity across landscapes. We collected the butterfly Coenonympha pamphilus in four replicated landscape pairs, each consisting of (a) a highly fragmented and intensified ‘modern’ and (b) a less fragmented ‘traditional’ agricultural landscape. We compared condition (i.e. storage reserves), flight morphology, dispersal capacity and propensity of the collected butterflies between both landscape types. We also tested for the impact of landscape composition and configuration at different spatial scales on butterfly traits. No differences between landscape types per se could be found, but a variety of landscape features affected butterfly traits, indicating complex interactions between landscape heterogeneity and dispersal. In particular, landscapes with a high proportion of crop fields appeared to be selected for phenotypes enhancing dispersal ability. Since dispersal is a key factor for the persistence of metapopulations in fragmented landscapes, we argue that limitations on dispersal in relation to compositional and configurational landscape heterogeneity should be considered in the debate on insect declines in agricultural landscapes.

The evolution of passive dispersal versus habitat selection have differing emergent consequences in metacommunities.

Dispersal among local communities is fundamental to the metacommunity concept but is only important to the metacommunity structure if dispersal causes distortions of species abundances away from what local ecological conditions favour. We know from much previous work that dispersal can cause such abundance distortions. However, almost all previous theoretical studies have only considered one species alone or two interacting species (e.g. competitors or predator and prey). Moreover, a systematic analysis is needed of whether different dispersal strategies (e.g. passive dispersal versus demographic habitat selection) result in different abundance distortion patterns, how these distortion patterns change with local food web structure, and how the dispersal propensities of the interacting species might evolve in response to one another. In this article, we show using computer simulations and analytical models that abundance distortions occur in simple food webs with both passive dispersal and habitat selection, but habitat selection causes larger distortions. Additionally, patterns in the evolution of dispersal propensity in interacting species are very different for these two dispersal strategies. This study identifies that the dispersal strategies employed by interacting species critically shape how dispersal will influence metacommunity structure. This article is part of the theme issue 'Diversity-dependence of dispersal: interspecific interactions determine spatial dynamics'.

Life history correlations and trade-offs resulting from selection for dispersal in Tribolium castaneum.

Dispersal is an important facet of the life history of many organisms and is, therefore, subject to selective pressure but does not evolve in isolation. Across nature, there are examples of dispersal syndromes and life history strategies in which suites of traits coevolve and covary with dispersal in combinations that serve to maximize fitness in a given ecological context. The red rust flour beetle, Tribolium castaneum, is a model organism and globally significant post-harvest pest that relies on dispersal to reach new patches of ephemeral habitat. Dispersal behaviour in Tribolium has a strong genetic basis. However, a robust understanding of the relationship between dispersal and other life-history components, which could elucidate evolutionary processes and allow pest managers to control their spread and reduce the impact of infestation, is currently lacking. Here, we use highly replicated lines of T. castaneum previously artificially selected for divergent small-scale dispersal propensity to robustly test several important life history components: reproductive strategy, development time, and longevity. As predicted, we find that a suite of important changes as a result of our selection on dispersal: high dispersal propensity is associated with a lower number of longer mating attempts by males, lower investment in early life reproduction by females, slower development of later-laid offspring, and longer female life span. These findings indicate that correlated intraspecific variation in dispersal and related traits may represent alternative life history strategies in T. castaneum. We therefore suggest that pest management efforts to mitigate the species' agro-economic impact should consider the eco-evolutionary dynamics within multiple life histories. The benefits of doing so could be felt both through improved targeting of efforts to reduce spread and also in forecasting how the selection pressures applied through pest management are likely to affect pest evolution.

Higher trophic levels and species with poorer dispersal traits are more susceptible to habitat loss on island fragments.

Ongoing habitat loss and fragmentation caused by human activities represent one of the greatest causes of biodiversity loss. However, the effects of habitat loss and fragmentation are not felt equally among species. Here, we examined how habitat loss influenced the diversity and abundance of species from different trophic levels, with different traits, by taking advantage of an inadvertent experiment that created habitat islands from a once continuous forest via the creation of the Thousand Island Lake, a large reservoir in China. On 28 of these islands with more than a 9000-fold difference in their area (0.12-1154 ha), we sampled plants, herbivorous insects, and predatory insects using effort-controlled sampling and analyses. This allowed us to discern whether any observed differences in species diversity were due to passive sampling alone or to demographic effects that disproportionately influenced some species relative to others. We found that while most metrics of sampling effort-controlled diversity increased with island area, the strength of the effect was exacerbated for species in higher trophic levels. When we more explicitly examined differences in species composition among islands, we found that the pairwise difference in species composition among islands was dominated by species turnover but that nestedness increased with differences in island area, indicating that some species are more likely to be absent from smaller islands. Furthermore, by examining trends of several dispersal-related traits of species, we found that species with lower dispersal propensity tended to be those that were lost from smaller islands, which was observed for herbivorous and predatory insects. Our results emphasize the importance of incorporating within-patch demographic effects, as well as the taxa and traits of species when understanding the influence of habitat loss on biodiversity.

Effects of increasing soil moisture on Antarctic desert microbial ecosystems.

Overgeneralization and a lack of baseline data for microorganisms in high-latitude environments have restricted the understanding of the microbial response to climate change, which is needed to establish Antarctic conservation frameworks. To bridge this gap, we examined over 17,000 sequence variants of bacteria and microeukarya across the hyperarid Vestfold Hills and Windmill Islands regions of eastern Antarctica. Using an extended gradient forest model, we quantified multispecies response to variations along 79 edaphic gradients to explore the effects of change and wind-driven dispersal on community dynamics under projected warming trends. We also analyzed a second set of soil community data from the Windmill Islands to test our predictions of major environmental tipping points. Soil moisture was the most robust predictor for shaping the regional soil microbiome; the highest rates of compositional turnover occurred at 10-12% soil moisture threshold for photoautotrophs, such as Cyanobacteria, Chlorophyta, and Ochrophyta. Dust profiles revealed a high dispersal propensity for Chlamydomonas, a microalga, and higher biomass was detected at trafficked research stations. This could signal the potential for algal blooms and increased nonendemic species dispersal as human activities increase in the region. Predicted increases in moisture availability on the Windmill Islands were accompanied by high photoautotroph abundances. Abundances of rare oligotrophic taxa, such as Eremiobacterota and Candidatus Dormibacterota, which play a crucial role in atmospheric chemosynthesis, declined over time. That photosynthetic taxa increased as soil moisture increased under a warming scenario suggests the potential for competition between primary production strategies and thus a more biotically driven ecosystem should the climate become milder. Better understanding of environmental triggers will aid conservation efforts, and it is crucial that long-term monitoring of our study sites be established for the protection of Antarctic desert ecosystems. Furthermore, the successful implementation of an improved gradient forest model presents an exciting opportunity to broaden its use on microbial systems globally.

Digest: Islands promote population differentiation in dispersive swallows.

How can highly dispersive species give rise to genetically distinct populations? This seemingly paradoxical pattern is common among insular birds, but not in those with continental distributions. Broyles and Myers sequence the genomes of almost 150 individuals from the island-dwelling Pacific swallow (Hirundo tahitica) and its continental counterpart, the welcome swallow (H. neoxena). They find strong population structure only among island populations and attribute this to a behavioral reduction in dispersal propensity following island colonization. However, wing shape remains consistent across populations, suggesting it might not accurately reflect dispersal propensity in this group. This study illustrates the interplay between dispersal, isolation, and divergence, offering insights into how geographic factors affect speciation and population differentiation on islands.

Evolutionarily labile dispersal behavior and discontinuous habitats enhance population differentiation in island versus continentally distributed swallows.

The causes of population divergence in vagile groups remain a paradox in evolutionary biology: dispersive species should be able to colonize new areas, a prerequisite for allopatric speciation, but dispersal also facilitates gene flow, which erodes population differentiation. Strong dispersal ability has been suggested to enhance divergence in patchy habitats and inhibit divergence in continuous landscapes, but empirical support for this hypothesis is lacking. Here we compared patterns of population divergence in a dispersive clade of swallows distributed across both patchy and continuous habitats. The Pacific Swallow (Hirundo tahitica) has an insular distribution throughout Southeast Asia and the Pacific, while its sister species, the Welcome Swallow (H. neoxena), has a continental distribution in Australia. We used whole-genome data to demonstrate strong genetic structure and limited introgression among insular populations, but not among continental populations. Demographic models show that historic changes in habitat connectivity have contributed to population structure within the clade. Swallows appear to exhibit evolutionarily labile dispersal behavior in which they reduce dispersal propensity after island colonization despite retaining strong flight ability. Our data support the hypothesis that fragmented habitats enhance population differentiation in vagile groups, and suggest that labile dispersal behavior is a key mechanism underlying this pattern.

Dispersal in Kentish Plovers (Charadrius alexandrinus): adult females perform furthest movements

Dispersal is an important behavioral process that plays a significant role in, among others, speciation, population viability, and individual fitness. Despite progress in avian dispersal research, there are still many knowledge gaps. For example, it is of interest to study how dispersal propensity relates to age- and/or sex-specific patterns. Here, we investigated the role of sex and life stage on natal (i.e., movement from birth site to first breeding site) and breeding dispersal (i.e., movement between sequential breeding sites) in the Kentish Plover (Charadrius alexandrinus) for dispersal events of more than 10 km. This small and inconspicuous wader is characterized by flexible mating behavior that includes monogamy, and serial polygynandry. Using a continent-wide dataset of ringing and re-encounter data throughout the species’ range in Europe, we found that adult females generally dispersed further than adult males between seasons, but we detected no sex difference in natal dispersal distances and no general difference between natal and breeding dispersal distances. Furthermore, females were the main group exhibiting ‘long-distance’ breeding dispersal, which we defined as dispersal greater than ≥ 108 km, i.e., the upper 10% percentile of our dataset. The data set included dispersal of two females that first bred in the Mediterranean before being detected breeding at the North Sea in the subsequent year, having dispersed 1290 and 1704 km, respectively. These observations represent the longest breeding dispersal observed within the genus Charadrius. Our long-distance dispersal records are consistent with low genetic differentiation between mainland populations shown in previous work. The dispersal of the Kentish Plover is likely linked to its breeding behavior: polyandrous females exhibit extensive mate searching and habitat prospecting. We recommend that the dispersal traits of Kentish Plover be incorporated into the species’ conservation and management planning to more accurately inform models of population connectivity and metapopulation dynamics.

Candidate gene polymorphisms are linked to dispersive and migratory behaviour: Searching for a mechanism behind the "paradox of the great speciators".

The "paradox of the great speciators" has puzzled evolutionary biologists for over half a century. A great speciator requires excellent dispersal propensity to explain its occurrence on multiple islands, but reduced dispersal ability to explain its high number of subspecies. A rapid reduction in dispersal ability is often invoked to solve this apparent paradox, but a proximate mechanism has not been identified yet. Here, we explored the role of six genes linked to migration and animal personality differences (CREB1, CLOCK, ADCYAP1, NPAS2, DRD4, and SERT) in 20 South Pacific populations of silvereye (Zosterops lateralis) that range from highly sedentary to partially migratory, to determine if genetic variation is associated with dispersal propensity and migration. We detected genetic associations in three of the six genes: (i) in a partial migrant population, migrant individuals had longer microsatellite alleles at the CLOCK gene compared to resident individuals from the same population; (ii) CREB1 displayed longer average microsatellite allele lengths in recently colonized island populations (<200 years), compared to evolutionarily older populations. Bayesian broken stick regression models supported a reduction in CREB1 length with time since colonization; and (iii) like CREB1, DRD4 showed differences in polymorphisms between recent and old colonizations but a larger sample is needed to confirm. ADCYAP1, SERT, and NPAS2 were variable but that variation was not associated with dispersal propensity. The association of genetic variants at three genes with migration and dispersal ability in silvereyes provides the impetus for further exploration of genetic mechanisms underlying dispersal shifts, and the prospect of resolving a long-running evolutionary paradox through a genetic lens.

No impact of habitat fragmentation on condition and dispersal ability in the highly mobile butterfly Pieris rapae

AbstractThe loss and fragmentation of natural habitats due to agricultural intensification have a strong negative impact on farmland biodiversity. The concomitant isolation of essential resources may exert selection pressures toward increased dispersal performance in flying insects, possibly resulting in differences in flight morphology and dispersal propensity across landscapes. Here, we compared condition, flight morphology, dispersal capacity, and propensity of the common butterfly Pieris rapae among four pairs of highly fragmented “modern” and less fragmented “traditional” agricultural landscapes. We did not find differences between landscape types, but between locations and sexes. These results are not entirely unexpected, as P. rapae is a highly mobile generalist species, able to exploit temporarily available resources such as rapeseed in modern agricultural landscapes. In addition, our negative results may suggest a lack of time for evolutionary change such that differences may appear in the future. However, more specialized species with low dispersal ability may show clearer patterns and may well suffer from habitat fragmentation, and investigating such interrelation is an important task for future research.

Behavioural profiles in a wild population of a cooperatively breeding cichlid

AbstractIn cooperatively breeding species, subordinates can obtain group membership through social interactions with other group members or by providing services such as helping with territory defence. Large subordinate individuals, which can reproduce, are expected to adjust their behaviour as a function of the demand of help and group size because if the environmental conditions allow, they may either leave the group to start breeding or queue for the breeding position in their natal group. The number of helpers in a group is expected to affect the need of help by dominants and consequently also the level of subordination shown by helpers. In a series of field experiments, we manipulated the need of help and the opportunities for subordinates to show submissive behaviour in a wild population of the cooperatively breeding species Neolamprologus pulcher. We assessed if group size determines the social behavioural strategy of large subordinate individuals. When experimentally eliciting submissive behaviour, large subordinates from small groups showed a lower frequency of submissive behaviour compared to large groups; moreover, they tended to show a higher frequency of sand digging than in large groups. In contrast, neither territory defence in the presence of a heterospecific egg and larvae predator nor dispersal propensity, measured as prospecting frequency in neighbouring territories, was affected by group size. A principal component analysis revealed that prospecting is uncorrelated with submissive behaviour and helping behaviour. Our results suggest that group size may be involved in shaping behavioural phenotypes of juvenile subordinates.

Phylogenetic and functional trait-based community assembly within Pacific Cyrtandra (Gesneriaceae): Evidence for clustering at multiple spatial scales.

Tropical rainforest communities are often characterized by a small number of species-rich genera that contribute disproportionately to the alpha diversity in these habitats. In the Pacific Basin, there are nearly 200 species of Cyrtandra, most of which are white-flowered woody shrubs that are single-island endemics. Within these island communities, multiple Cyrtandra species are commonly observed to occur sympatrically in wet forest understories, forming swarms of what appear to be ecologically similar taxa. The aim of this study was to determine whether species of these plants are randomly assembled with respect to phylogenetic relatedness and traits that are ecologically relevant. I examined assembly patterns across three Pacific archipelagoes using a combination of 10 functional traits and a well-resolved phylogeny comprising 34 species of Cyrtandra. Coexisting species were found to be more closely related and more phenotypically similar than would be expected by chance. This pattern was observed at both regional (island) and local (site) spatial scales. The retention of phylogenetic signal in floral traits and the strong influence of these traits on the observed degree of phylogenetic clustering may indicate that generalist insect pollinators act as a biotic filter on oceanic islands, driving selection for similar floral morphology among closely related species of Pacific Cyrtandra. Phylogenetic signal was also detected in leaf size, which contributed to niche clustering at both spatial scales. Coupled with a propensity for long-distance dispersal, and the restricted distribution of Cyrtandra to rainforest understories, this finding suggests that environmental filtering along this trait axis may be more important than dispersal limitation in determining species assemblages. This study supports the theory that plant species are not randomly assembled, and instead, that niche-based processes structure biodiversity at regional and local spatial scales in diverse congeneric species assemblages.

Range expansions of sexual versus asexual organisms: Effects of reproductive assurance and migration load.

It is generally considered that sexual organisms show faster evolutionary adaptation than asexual organisms because sexuals can accumulate adaptive mutations through recombination. Yet, empirical evidence often shows that the geographic range size of sexual species is narrower than that of closely related asexual species, which may seem as if asexuals can adapt to more varied environments. Two potential explanations for this apparent contradiction considered by the existing theory are reproduction assurance and migration load. Here, we consider both reproductive assurance and migration load within a single model to comparatively examine their effects on range expansions of sexuals and asexuals across an environmental gradient. The model shows that higher dispersal propensity decreases sexuals' disadvantage in reproductive assurance while increasing their disadvantage in migration load. Moreover, lower mutation rate constrains adaptation more strongly in asexuals than in sexuals. Thus, high dispersal propensity and high mutation rates promote that asexuals have wider range sizes than sexuals. Intriguingly, our model reveals that sexuals can have wider geographic range sizes than asexuals under low dispersal propensity and low mutation rates, a pattern consistent with a few exceptional empirical cases. Combining reproductive assurance and migration load provides a useful perspective to better understand the relationships between species' mating systems and their geographic ranges.

Gondwanan origin of the Dipterocarpaceae-Cistaceae-Bixaceae is supported by fossils, areocladograms, ecomorphological traits and tectonic-plate dynamics

There is disparity between the estimated time of origin of the ‘superclade’ Dipterocarpaceae sensu lato, that includes Sarcolaenaceae, Cistaceae, Pakaraimaea, Bixaceae, Cochlospermaceae and Sphaerosepalaceae, as determined by recent molecular phylogenies (100−85 million years ago, Ma) and its strongly tropical, South American-African-Madagascan-SE Asian distribution that indicates an older Gondwanan origin (&gt;110 Ma). We used several paleobiogeographic approaches, including recently reported fossil records, to explore the hypothesis that Dipterocarpaceae sl has a Gondwanan/early-Cretaceous origin.We created molecular phylogenies for this group, assigned each genus/family to the tectonic plate on which it is extant, and subjected the cladogram to areogram analysis. We also assessed ecological, mycotrophic and morphological traits, and global circulation patterns, as these might affect this group’s distribution.The initial analysis (omitting fossil evidence) showed that the crown of Dipterocarpaceae sl occurred concurrently on the South American and Madagascan plates. Including fossils from Africa and India changed this to a South American-African origin. Collectively, these origins represent NorthWest Gondwana with South America, Africa and Madagascar remaining conjoined until ≥105–115 Ma, setting the minimum age for this superclade with some evidence that it may be much older. We also show that the immediate ancestors of the three daughter lineages [Dipterocarpaceae- Sarcolaenaceae (in Africa/Madagascar, ≥115 Ma), Cistaceae- Pakaraimaea (South America/Africa/Eurasia, ≥105 Ma) and Bixaceae-Cochlospermum-Sphaerosepalaceae (South America/ Africa, ≥105 Ma)] also arose in NorthWest Gondwana.The immediate ancestors or basal species in Sarcolaenaceae, Sphaerosepalaceae, Dipterocarpaceae (both its subfamilies) and Bixaceae migrated from (South America)/Africa to Madagascar and we propose that the Dipterocarpoideae proceeded from Africa to India while still linked to Madagascar. In addition, much subsequent diversification of this superclade has occurred on the Eurasian, Indian, SE Asian (Sunda) and North American plates post-Gondwanan breakup.This long vicariant history is supported by fossil, ecological, mycotrophic and morphological traits, and global circulation patterns that show negligible propensity for transoceanic dispersal to explain this clade’s wide intercontinental distribution.We conclude that all these areocladogram/plate-breakup/ ecomorphological/circulation features are consistent with a Gondwanan/early-Cretaceous (&gt;115 Ma) origin for the Dipterocarpaceae-Cistaceae-Bixaceae superclade plus its three daughter clades. Future analyses at the species level, exploring alternative diversification dates from both fossils and plate-tectonic dynamics, are needed to refine these findings.

Accelerated invasion through the evolution of dispersal behaviour

AbstractAimThe continuous spread of invasive species is attributed to demographic processes and high dispersal rates. Both can change and evolve during range expansion, eventually accelerating spread dynamics. Here, we document such an accelerated spread for one of the most invasive spiders in Europe, the dwarf spider Mermessus trilobatus, and test whether dispersal, reproduction or competitive ability is at the source of this pattern.LocationEurope.Time period1981–2021.Major taxon studiedMermessus trilobatus (Arachnida: Araneae: Linyphiidae).MethodsFirst, we collected records from 21 countries across Europe to document the speed of progression of the invasion front over the last 40 years. Second, we collected live individuals from populations in the longest and more recently invaded areas and compared the dispersal propensity of offspring raised under standardized conditions. Third, we compared the reproduction and competitive ability of females derived from the populations of long‐invaded areas against areas with more recent establishment.ResultsThe progression of the invaded range increased from about 150 km in the 1980s to some 400 km between 2010 and 2020. Dispersal‐related behaviour was nearly twice as frequent in offspring from invasion front populations compared to the core area. By contrast, we found no differences in reproduction or competitive ability among the studied populations. Further, neither joint inheritance nor trade‐offs of dispersal, reproduction or competitive ability were identified.Main conclusionAs high dispersal is recessively inherited in M. trilobatus, our results suggest that the accelerated invasion is due to the accumulation of dispersive but not more reproductive or competitive genotypes in newly colonized areas. Given the high climatic amplitude of the species in North America, we expect it to spread over the remaining parts of Europe and large parts of Asia in the coming decades. Accelerated range expansion through the evolution of dispersal behaviour could play a role in numerous arthropod invasions worldwide.

Locations of seed abortion in response to defoliation differ with pollen source in a native perennial legume herb.

In many flowering plants, flowers contain more ovules than fruits have seeds. What determines which ovules become seeds? When photosynthates are limited, as may happen when plants lose leaf area to herbivory, fewer fertilized ovules become seeds. Greenhouse-grown ramets of distinct individuals of a perennial herbaceous legume were manually defoliated to various levels determined in the field, then self- or cross-pollinated. For each seed produced, we recorded its position in the fruit and its mass. From a subset of seeds from different treatments and positions in the fruits, we grew seedlings and measured their dry mass. Ovules were aborted more frequently in fruits from flowers that were self-pollinated and from those on plants with higher levels of defoliation. Ovules in the basal portion of the fruits were more likely to be aborted than those at the stigmatic end; this pattern was most pronounced for fruits after self-pollination with high levels of defoliation. Total number of seeds produced and seed mass per pod were greatest in cross-pollinated fruits after no or low levels of defoliation. Mean individual seed mass was greater for fruits with fewer seeds, indicating a trade-off between seed number and seed mass. Seedling dry mass (a measure of vigor) was greatest for seeds in the middle positions of fruit produced by cross-pollination after severe herbivory; no positional differences were seen for seeds from self-pollinated fruits. Observed locations of seed abortion may have been selected not only by defoliation, but in part by propensity for dispersal, while positional differences in seedling vigor may be related to seed size and differential maternal allocation based on pollination treatment and leaf area lost.

Analysis of the Holarctic Dictyoptera aurora Complex (Coleoptera, Lycidae) Reveals Hidden Diversity and Geographic Structure in Müllerian Mimicry Ring.

The elateroid family Lycidae is known for limited dispersal propensity and high species-level endemism. The red net-winged beetle, Dictyoptera aurora (Herbst, 1874), differs from all relatives by the range comprising almost the entire Holarctic region. Based on a five-marker phylogeny and 67 barcode entries (cox1-5' mtDNA) from the whole range, we recovered two genetically distinct species within traditionally defined D. aurora and resurrected the name D. coccinata (Say, 1835) as the oldest available synonym for Nearctic populations. Yet, no reliable morphological trait distinguishes these species except for minute differences in the male genitalia. D. coccinata is a monophylum resulting from a single Miocene dispersal event, ~15.8 million years ago, and genetic divergence implies long-term isolation by the Bering Strait. Far East Asian and west European populations are also genetically distinct, although to a lower extent. Two independent colonization events established the Fennoscandian populations after the last glacial maximum. Besides intrinsic factors, the high morphological similarity might result from stabilizing selection for shared aposematic signals. The rapidly accumulating barcode data provide valuable information on the evolutionary history and the origins of regional faunas.

Genetic Structure and Colonization of North America by Depressaria depressana (Fabricius 1775) (Lepidoptera: Depressariidae) over 15 Years; Contrasts with Westward Expansion of Depressaria radiella (Goeze, 1783) over 160 Years.

Simple SummaryAs invasive insect species can disrupt agriculture, ecosystem functions, and human health, monitoring the spread of newly invasive insects is a high priority. The purple carrot-seed moth Depressaria depressana, a European species first reported in North America in 2008, specializes on reproductive structures of taxa throughout the family Apiaceae and thus presents a potential threat to native North American umbellifers. We assessed interpopulational genetic diversity of D. depressana across its eastern North American invasion front and compared those values to available data for European populations. We also compared this diversity with genetic diversity estimates for populations of Depressaria radiella (parsnip webworm), a European species introduced to North America more than 160 years ago that is essentially restricted to two apiaceous genera throughout its native and invasive ranges. Documenting the historical spread of D. radiella with museum and literature records, we found D. depressana displays greater genetic diversity than D. radiella and is colonizing North America more rapidly; greater genetic diversity may facilitate faster colonization via establishment on a wider range of hostplants. The contrast in colonization by these two species may inform management practices for invasive insects utilizing a broad versus narrow array of hosts within a single plant family.Depressaria depressana, the purple carrot seed moth, is a Eurasian species first reported in North America in 2008 and currently undergoing range expansion. This invasion follows that of its Eurasion congener Depressaria radiella (parsnip webworm), first documented in North America 160 years ago. Unlike D. depressana, which utilizes hostplants across multiple tribes of Apiaceae, Depressaria radiella is a “superspecialist” effectively restricted in its native and non-indigenous ranges to two closely related apiaceous genera. We investigated the genetic structure of D. depressana populations across latitudinal and longitudinal gradients in the eastern United States by constructing COI haplotype networks and then comparing these with haplotype networks constructed from available COI sequence data from contemporary European D. depressana populations and from European and North American D. radiella populations. Haplotype data revealed higher genetic diversity in D. depressana, indicating high dispersal capacity, multiple introductions, and/or a genetically diverse founding population. Museum and literature records of D. radiella date back to 1862 and indicate that range expansion to the West Coast required more than 50 years. Higher levels of genetic diversity observed in D. depressana compared to its congener may indicate a greater propensity for dispersal, colonization and establishment in its non-indigenous range.