Dispersal Morphology Research Articles

Sex specificity of dispersal behaviour and flight morphology varies among tree hollow beetle species

BackgroundFlight performance and dispersal behaviour can differ between sexes, resulting in sex-biased dispersal. The primary sex ratio of populations may also explain dispersal bias between sexes, as this bias may evolve with the primary sex ratio to reduce intrasexual competition. Although dispersal bias between sexes is relevant to population dynamics, there are few studies on sex-biased dispersal in insects. We studied the flight performance and dispersal behaviour of seven saproxylic beetle species associated with tree hollows from a sex perspective. We also analysed the possible coevolution of flight performance with the primary sex ratio.MethodsWing loading and wing aspect ratio were used as measures of the flight performance of species and sexes. Dispersal behaviour was explored by analysing the frequency of each sex in interception traps versus the primary sex ratio obtained by tree hollow emergence traps using contingency tables and posthoc standardized residuals. A more active flight behaviour was expected for the sex with higher capture frequency in the interception traps. To explore the causes of flight performance bias between sexes, we searched for possible correlations between wing loading or wing aspect ratio and primary sex ratio using Pearson’s correlation coefficient.ResultsWing loading and wing aspect ratio differed between species and sexes, with flight performance being higher in males than in females for four of the seven species analysed. Dispersal behaviour and flight performance matched in the case of Elater ferrugineus; males showed higher flight performance and were the most collected sex in the interception traps (more active flyers). In contrast, the higher flight activity of Cetonia carthami aurataeformis females was not correlated with a higher flight performance than that of males. Moreover, we found that a bias in the primary sex ratio towards females is often correlated with a decrease in female flight performance.ConclusionsWe stress that flight performance and dispersal behaviour of sexes do not always go hand in hand. Moreover, the relationship between the sex ratio and flight performance bias between sexes is not driven by competition within the most abundant sex. The inclusion of a sex perspective in insect dispersal studies would be useful to detect dispersal bias between sexes and its causes and would allow for further analysis of its effects on population dynamics.

Pantropical diversification of padauk trees and relatives was influenced by biome‐switching and long‐distance dispersal

AbstractAimPhenotypes promoting dispersal over ecological timescales may have macroevolutionary consequences, such as long‐distance dispersal and diversification. However, whether dispersal traits explain the distribution of pantropical plant groups remains unclear. Here we reconstruct the biogeographical history of a tree clade to assess whether seed dispersal traits and biome‐switching explain the clade’s pantropical distribution.LocationPantropical.TaxonThe Pterocarpus clade (Leguminosae/Fabaceae).MethodsWe sequenced 303 nuclear loci using target capture and generated a time‐calibrated phylogenomic tree. We also generated a corroborative time‐calibrated phylogenetic tree from data‐mined Sanger‐sequencing data. We then collated distribution data and seed dispersal morphology traits to compare trait‐dependent and trait‐independent biogeographical models, allowing us to infer whether dispersal traits influenced Pterocarpus’ spatio‐temporal evolution. Finally, using the results of these model tests, we estimated the ancestral ranges and biomes of Pterocarpus species to better understand their biogeographical history, and assessed the degree and direction of biome‐switching over the course of their diversification.ResultsWe recovered well‐supported phylogenetic relationships within Pterocarpus, within which there were two subclades – one neotropical and the other palaeotropical. Our divergence date estimates suggested that Pterocarpus diversified from around 12 Ma, during the Miocene. Trait‐dependent biogeographical models were rejected for both range and biome evolution within Pterocarpus, but models including dispersal were supported. Pterocarpus’ ancestral node shared a range across the new‐world and old‐world tropics, followed by divergence into palaeotropical and neotropical clades. Biome‐switching occurred most frequently into rainforest and grassland.Main conclusionsOur analyses suggest that Pterocarpus underwent infrequent cross‐continental dispersal and establishment into novel biomes. While this was minimally impacted by seed dispersal traits, biome‐switching following long‐distance dispersal and climate change have played an important role in diversification within Pterocarpus since the Miocene. Indeed, rare events of long‐distance dispersal likely explain the wide distributions of many pantropical plant species.

Predation risk differentially affects aphid morphotypes: impacts on prey behavior, fecundity and transgenerational dispersal morphology

To avoid predation, prey initiate anti-predator defenses such as altered behavior, physiology and/or morphology. Prey trait changes in response to perceived predation risk can influence several aspects of prey biology that collectively contribute to individual success and thus population growth. However, studies often focus on single trait changes in a discrete life stage or morphotype. We assessed how predation risk by Harmonia axyridis affects several important traits in the aphid, Myzus persicae: host plant preference, fecundity and investment in dispersal. Importantly, we examined whether these traits changed in a similar way between winged (alate) and wingless (apterous) adult aphid morphotypes, which differ in morphology, but also in life-history characteristics important for reproduction and dispersal. Host plant preference was influenced by the presence of H.axyridis odors in choice tests; wingless aphids were deterred by the odor of plants with H.axyridis whereas winged aphids preferred plants with H.axyridis present. Wingless aphids reared in the presence of ladybeetle cues produced fewer offspring in the short-term, but significantly more when reared with exposure to predator cues for multiple generations. However, winged aphid fecundity was unaffected by H.axyridis cues. Lastly, transgenerational plasticity was demonstrated in response to predation risk via increased formation of winged aphid morphotypes in the offspring of predator cue-exposed wingless mothers. Importantly, we found that responses to risk differ across aphid polyphenism and that plasticity in aphid morphology occurs in response to predation risk. Together our results highlight the importance of considering how predation risk affects multiple life stages and morphotypes.

The evolution of seed dispersal is associated with environmental heterogeneity in Pinus

Seed dispersal is a major life history stage for plants. Because of its influence on reproductive success, dispersal is expected to be under strong selection. Different ecological circumstances might favour dispersal towards few suitable sites or alternatively, the random distribution of propagules among suitable and unsuitable sites. However, the evolutionary dynamics favouring specific dispersal syndromes remain a matter of speculation in many cases. Here, we explore the linkage between dispersal and environmental conditions at an evolutionary scale. We use a comparative phylogenetic approach to investigate the evolution of dispersal morphology in the genus Pinus and its connection with climatic variability, aridity and fire. Our results show that dispersal appears to have evolved towards two alternative strategies: seeds with vs. without wings, closely matching the distribution of wind- and vertebrate- mediated dispersal within the genus. Moreover, we find a close evolutionary association between dispersal morphology and environmental conditions such that each morphology predominates under particular abiotic conditions. Seeds with bigger wings are selected for primarily in environments with high temperature variability and/or prone to fire, whereas wingless or remnant-winged seeds are evolutionarily linked primarily to environments that are arid or exhibit a high variability in rainfall. These findings suggest a role of seed dispersal in the adaptation to certain environmental conditions, along with the influence of such conditions on the evolution of plant functional traits.

Harbor seal pup dispersal and individual morphology, hematology, and contaminant factors affecting survival

AbstractUnderstanding the factors affecting individual harbor seal (Phoca vitulina) survival is essential for determining population level health risks. We estimated postweaning dispersal, and modeled the effects of morphology, hematology, and blubber contaminants on the survival of recently weaned harbor seal pups using a mark recapture framework. We deployed satellite transmitters on apparently healthy pups captured in San Francisco Bay (SFB, n = 19) and Tomales Bay (TB, n = 7), and pups released after rehabilitation that stranded along the central California coast preweaning (n = 21). Dispersal distances were further than previously reported for harbor seal pups (maximum = 802 km) which has implications for understanding risks to this vulnerable age class. We found differences in body condition, serum immunoglobulin and thyroxine (T4) concentrations, white blood cell count, and blubber organohalogen contamination (OH) among the three groups. Overall, increased T4, decreased OH, and increased mass were associated with greater survival probabilities; whereas, among stranded seals, greater mass gain, shorter time in rehabilitation, and admission to rehabilitation earlier in the season were associated with greater survival probabilities. Attention to these latter factors may improve the success of rehabilitation efforts. For wild pups, reduction of legacy contaminants and direct causes of mortality, such as ship strike, may enhance pup survival.

Redescription of Bursaphelenchus eucarpus Rühm, 1956 (Nematoda: Aphelenchoididae) associated with the apple bark beetle, Scolytus mali Bechstein, and the shothole borer, S. rugulosus Müller

Summary New morphological, molecular and bionomic data are added to update the description of Bursaphelenchus eucarpus. The nematode was isolated from larval galleries and adults of the apple bark beetle, Scolytus mali, and the shothole borer, S. rugulosus, present under the bark of the bird cherry, Prunus padus, and the common European plum, P. domestica, in Poland. Detailed male, female and dispersal juvenile morphology and morphometrics are documented and compared with the original description. From partial 18S, ITS1/2 and partial 28S D2-D3 sequences and morphological features (three lateral lines, position of caudal papillae, shape of the delicate spicules with dorsally bent condylus, lack of vulval flap, a long post-uterine branch and a hyaline region at the female tail tip) it can be concluded that B. eucarpus belongs to the eremus group of Bursaphelenchus. The differentiation from related species of the eremus group is discussed.

Life History Consequences of the Facultative Expression of a Dispersal Life Stage in the Phoretic Bulb Mite (Rhizoglyphus robini).

Life history traits play an important role in population dynamics and correlate, both positively and negatively, with dispersal in a wide range of taxa. Most invertebrate studies on trade-offs between life history traits and dispersal have focused on dispersal via flight, yet much less is known about how life history trade-offs influence species that disperse by other means. In this study, we identify effects of investing in dispersal morphology (dispersal expression) on life history traits in the male dimorphic bulb mite (Rhizoglyphus robini). This species has a facultative juvenile life stage (deutonymph) during which individuals can disperse by phoresy. Further, adult males are either fighters (which kill other mites) or benign scramblers. Here, in an experiment, we investigate the effects of investing in dispersal on size at maturity, sex and male morph ratio, and female lifetime reproductive success. We show that life history traits correlate negatively with the expression of the dispersal stage. Remarkably, all males that expressed the dispersal life stage developed into competitive fighters and none into scramblers. This suggests that alternative, male reproductive strategies and dispersal should not be viewed in isolation but considered concurrently.

Landscape configuration determines gene flow and phenotype in a flightless forest-edge ground-dwelling bush-cricket, Pholidoptera griseoaptera

Spatial configuration of habitats influences genetic structure and population fitness whereas it affects mainly species with limited dispersal ability. To reveal how habitat fragmentation determines dispersal and dispersal-related morphology in a ground-dispersing insect species we used a bush-cricket (Pholidoptera griseoaptera) which is associated with forest-edge habitat. We analysed spatial genetic patterns together with variability of the phenotype in two forested landscapes with different levels of fragmentation. While spatial configuration of forest habitats did not negatively affect genetic characteristics related to the fitness of sampled populations, genetic differentiation was found higher among populations from an extensive forest. Compared to an agricultural matrix between forest patches, the matrix of extensive forest had lower permeability and posed barriers for the dispersal of this species. Landscape configuration significantly affected also morphological traits that are supposed to account for species dispersal potential; individuals from fragmented forest patches had longer hind femurs and a higher femur to pronotum ratio. This result suggests that selection pressure act differently on populations from both landscape types since dispersal-related morphology was related to the level of habitat fragmentation. Thus observed patterns may be explained as plastic according to the level of landscape configuration; while anthropogenic fragmentation of habitats for this species can lead to homogenization of spatial genetic structure.

Caspase activation independent of cell death is required for proper cell dispersal and correct morphology in PC12 cells

Caspase activation is indispensable for the proper execution of apoptosis. However, to date, little is known about other possible physiologic functions for this class of enzymes in addition to their well-defined role in apoptosis. In this report, we described an action of caspase-3 involving cell dispersion that is independent of cell death. Using an in vitro neuronal model system consisting of PC12 cells, we observed a transient activation of caspase-3 both in situ and by Western blot analysis that was evident at 1 h following plating, was maximal by 3 h, and was attenuated by 24 h. Preincubation of PC12 cells with either the caspase-3 inhibitor, DEVD, or antisense caspase-3 oligonucleotides caused cells to be more rounded in appearance and led to a failure of cells to disperse properly. Additional experiments demonstrated a possible target for caspase cleavage to be the cytoskeletal protein, tau. These data suggest a requirement for caspase activation and subsequent disassembly of the cytoskeleton during cell dispersion and represent a novel role for caspases that may allow for proper migration of neurons to target locations during development.

Maternal size and stress and offspring philopatry: An experimental study in the common lizard (Lacerta vivipara)

:During gestation, many morphological, physiological, and behavioural traits are influenced by the maternal environment. Previous experiments on natal dispersal in Lacerta vivipara demonstrated that maternal condition during gestation affects juvenile dispersal behaviour. The mechanisms by which a female may influence her offspring, or offspring respond to changes in the mother’s internal environment, remain largely unknown. In this study, we investigated the role of corticosterone during pregnancy on the production of the dispersal phenotype. Ninety pregnant females were collected from a population at Cévennes (Massif Central) and kept in the laboratory until parturition. We applied a corticosterone solution daily on the back of 58 females and applied a similar solution, but without corticosterone, to the 32 others as a control. We measured dispersal propensity and morphology of the offspring of both groups. Morphology of offspring was not affected by hormonal treatment of their mothers, but dispersal of young from corticosterone-treated mothers was significantly smaller for large-sized (old) mothers and significantly greater for small-sized (young) females compared to the offspring of control females. Corticosterone might not be the only factor affecting the development of the juvenile dispersal phenotype. Maternal effects on juvenile dispersal reflect future survival prospects of the female and/or the quality of her environment; this finding strengthens our previous finding that natal dispersal in L. vivipara results from the integration of multiple factors.

Late Quaternary evolution of the Yellow/East China Sea tidal regime and its impacts on sediments dispersal and seafloor morphology

The evolution of a tidal-current field in the Yellow Sea and East China Sea (YECS) in response to the sea-level rise since the last glacial maximum (LGM) was investigated using a two-dimensional tidal model, with special attention to changes in the sedimentary environment of the continental shelf region. It was found that tidal currents on the YECS shelf have generally been semi-diurnal throughout the post glacial stages, with F-ratio (index of diurnal inequality) and S 2/M 2 ratio (index of spring–neap cycle) remaining similar to present. On the other hand, the spatial distribution of the tidal bottom stress associated with M 2 and M 4 tidal currents changed greatly during the transgression. As the sea level rose, two core regions showing high bottom-stress values migrated shoreward from Cheju Island toward the west coast of Korea, and along the retreat path of the paleo-Changjiang Estuary. Distribution of ‘extremely intense’ tidal bottom stress suggested that intense tidal reworking may have occurred at sea levels from −90 to −45 m in the southeast Yellow Sea and at −75 to −60 m off the paleo-Changjiang Estuary, the latter of which agreed with the timing of a large terrigenous organic C flux observed on the shelf slope. Distribution of slightly weaker bottom stress indicated that the sand ridges off the Changjiang Estuary and in the southeast Yellow Sea also might have formed at during those periods. On the other hand, when the sea level was between −45 and−15 m, the tidal bottom stress was generally not strong enough to invoke significant reworking, even though the stress intensity may be stronger than present. Correlation with modern and relict sedimentary features suggested that the tidal process have played a significant role on the reworking and deposition of sediments on the YECS shelf.

Characterizing plant attributes with particular emphasis on seeds in Tamaulipan thornscrub in semi-arid Mexico

Seed mass, dispersal syndromes and other plant attributes were investigated for 111 species native to north-eastern Mexico. We investigated whether seeds from Mexico conformed to patterns of seed size and dispersal syndrome spectra found for floras in arid environments from around the world. The distribution of seed mass in the Mexican flora (0·03–598 mg) was generally similar to that found elsewhere. All of the major seed dispersal syndromes previously found in arid environments were represented in Mexico, although vertebrate dispersal (33 species) was unusually common. There were 31 species having wind-dispersed seeds, four ant-dispersed and 43 with no obvious dispersal morphology. Woody species were more likely to have large seeds and herbaceous species were more likely to have small seeds. Woody plants had proportionally more wind-dispersed and less animal-dispersed species than did herbaceous plants. We did not find the expected relationship between time of seed set of vertebrate-dispersed species and the presence of migratory birds or between time of seed set and optimum germination time.

SPECIES IN THE TAIL OF RANK–ABUNDANCE CURVES

At focal sites within dry sclerophyll woodland and temperate rain forest, species were identified that were of low local abundance and hence in the tail of the rank–abundance curve. We then asked the question: What proportion of tail species within a given community are constitutive members of the tail everywhere throughout their geographical range, versus what proportion are found as substantially more abundant somewhere within their range? Out of 55 tail species identified from dry sclerophyll woodland and 116 tail species identified from temperate rain forest, 91% and 95%, respectively, were significantly more abundant at other locations (“somewhere-abundant” species), versus 9% and 5% “everywhere-sparse” species. Among eight attributes in dry sclerophyll woodland and nine attributes in temperate rain forest compared between somewhere-abundant and everywhere-sparse species, none discriminated consistently between the two groups of species. The size and dispersal morphology of seeds, flowering and fruiting durations and seasons, regeneration strategy after fire, size of geographical ranges, maximum plant height, and size class revealed no consistent distinctions. For the small minority of species that are everywhere-sparse, some general explanation may exist as to why they are in the tail of rank–abundance curves, though none was located among the attributes compared in this paper. For the majority of tail species that are somewhere-abundant, any explanation as to why they are in the tail will need to account for different outcomes in different places.

SEED MORPHOMETRICS AND ADAPTIVE GEOGRAPHIC DIFFERENTIATION.

Adaptive geographic differentiation is documented for seed morphology of 36 populations of Heterosperma pinnatum Cav. (Asteraceae), a seed heteromorphic annual plant in the central highlands of Mexico. Achenes (single-seeded fruits) vary continuously within heads but are classified by shape and position as central, intermediate, or peripheral morphs and as having adhesive awns or not. Here we quantify shape as a principal component score contrasting log length and width of achenes. Heads and their variation among populations are described in terms of maximum, minimum, and range of shape scores; the number of achenes per head; quantitative indices of the abruptness of shape shift; where in the head the most abrupt change in shape occurs; and what achene shapes have awns. First and second principal components of these descriptors summarize 86% of among-population variation in achene and head morphology and correlate strongly with percent central achenes per head (%C) and percent of achenes with awns (%A), respectively. Awns are associated with greater dispersibility and achene shape is correlated with speed of dormancy loss. We hypothesized that dispersal morphology would be associated with vegetation attributes indicative of population ephemerality and that dormancy morphology would be associated with precipitation patterns during the early germination season. Morphological distance matrices were calculated using Euclidean distances among populations in %A and %C. Geographic distances among populations were calculated, as were genetic distances based on isozyme frequencies from 29 bands of six enzymes. Vegetation was classified as open or closed and early spring (germination season) and summer precipitation means were determined for each site. Closed vegetation was assumed to provide only ephemeral habitats for H. pinnatum. Partial matrix correlations between morphology and environment controlled for geographic but not genetic distance among sites, since the latter was not significantly correlated with either morphology or geography. A significant relationship was found between %A and closed vegetation, lower spring, and higher summer precipitation. %C was only correlated with lower spring precipitation. Independence of isozyme and morphological traits is interpreted in terms of selection on the latter but not the former.

Reserve mass and dispersal investment in relation to geographic range of plant species: phylogenetically independent contrasts

Recent studies have reported conflicting evidence about correlations between seed size and plant species geographic range sizes. Using phylogenetically independent contrasts (PICs) within genera, we found no consistent differences in reserve mass between species with similar dispersal morphology and «wide» versus «narrow» geographic ranges. There was also no tendency within genera for broad ranged species to be those that allocate a larger percentage of the resources invested in each diaspora to dispersal structures. PICs were also constructed between species having a tenfold difference in seed size. In these PICs, the larger seeded species often occupied a greater number of regions than species with smaller seed sizes. This result was generated primarily through the comparison of species from different genera, families or higher level taxa which differed not only in seed mass but also in dispersal modes and growth forms. Finally, comparing species within Acacia and Eucalyptus having similar seed size but different dispersal modes, we found that bird dispersal (in Acacia) and possession of a wing for wind dispersal (in Eucalyptus) was associated with wider geographic range compared to lower‐investment dispersal modes. Taken together, these comparisons indicate that seed size is not itself important as a factor influencing breadth of geographic range. Dispersal mode and growth form may have an influence, however, and seed size differences may be associated with contrasts in dispersal mode or growth form.

Plant Life-History Attributes: Their Relationship to Disturbance Response in Herbaceous Vegetation

I Species composition and disturbance state (level of soil disturbance, grazing and water addition) were recorded for 120 (30-m2) plots in temperate grassland of the New England Tablelands (Australia). Three different classificatory schemes were used, based on (a) life-form (sensu Raunkiaer); (b) dispersal unit morphology and (c) vegetative reproduction. We analysed the effects of the different disturbance types and intensities on number and proportion of species belonging to these groups. The results were used to describe the spectrum of life-histories likely to be present at sites in different states of exogenous disturbance. 2 Soil disturbed sites had proportionately more therophytes, versatile/flat rosettes and wind dispersed species. Two features are likely to lead to success in soil disturbed sites: ability to colonize open space (e.g. therophytes, wind dispersal) and capacity to capture resources effectively (e.g. flat architecture of rosettes). Non-disturbed sites had more geophytes, chamaephytes, phanerophytes, proto-hemicryptophytes and erect rosettes, with greater numbers of vegetatively reproducing species. 3 Heavily grazed sites had higher proportions of therophytes and versatile/flat rosettes and species with mobile seeds than sites with light grazing. Moderately grazed sites had increased proportions of versatile and erect rosettes and more species with adhesive seeds (mainly grasses). Lightly grazed sites had a greater diversity in terms of evenness of all life-forms, dispersal morphologies and reproductive modes. 4 Water enriched sites had fewer geophytes and phanerophytes and some chamaephytes, erect rosettes and proto-hemicryptophytes. This loss was only partially compensated by a gain in versatile and partial rosettes but richness decreased overall. Water enrichment was unrelated to dispersal unit morphology or the potential for vegetative reproduction. 5 Of the three attributes examined, life-form was most useful in characterizing community response to different disturbance types. Traits related to regeneration (seed morphology and capacity of vegetative reproduction) were relevant to soil disturbance only. Our results support the use of such classifications for monitoring the effects of disturbance.

Geographic Ranges of Plant Species in Relation to Dispersal Morphology, Growth Form and Diaspore Weight

We investigated the relationship of geographic range to growth form, dispersal morphology and diaspore weight within three comparative databases of 219-325 native species from arid central Australia, semi-arid western NSW and maritime Sydney. Geographic range was measured as the number of regions occupied. In the arid and semi-arid floras, but not in the maritime flora, species adapted for dispersal by vertebrates (mainly birds) tended to occupy more regions than species adapted for dispersal by other means. The same pattern occurred within four major families (Chenopodiaceae, Myoporaceae, Mimosaceae and Solanaceae), and thus was not a product of differences between families. We suggest that lineages with adaptations for long-range dispersal may have undergone a lesser incidence of geographic speciation, within the arid and semi-arid flora.

Sand Dispersal at Norderneyer Seegat, West Germany: ABSTRACT

Norderneyer Seegat connects the North Sea and the Wattenmeer between the East Friesian Islands of Juist and Norderney. It is a high wave-energy mesotidal inlet. The mean tide range is 2.4 m and the estimated mean breaker height exceeds 1 m. The sediment dispersal pattern and resultant morphology differ significantly from those of mesotidal inlets investigated along the low wave-energy shores of the southeastern United States. The seaward margin of the ebb-tidal delta consists of a nearly continuous arc of bars, the reef-bow. These bars have segregated tidal flow; flood dominates a broad ramp facing into the dominant waves (i.e., the west side), ebb dominates the narrow steep leeside margin. The bars migrate eastward through combined tide and wave action at an average rate of 400 m/year. Bar migration appears to be the dominant mode of inlet sediment bypassing. The gorge section of the main inlet channel is ebb-dominated as a result of (1) water level-dependent inlet efficiency and (2) net water supply to the inlet drainage basin due to prevailing southwest winds. Flood-dominated intertidal sand shoals abound in, and landward of, the inlet gorge. Ebb-dominated flanks occur on some of the shoals. The degree of flood dominance increases landward, an effect which is attributed to the difference in celerity between the tidal wave trough and crest. Both the mechanics of ebb-delta sand bypassing, and the occurrence of tidal-flat flood dominance, distinguish the dispersal pattern at Norderneyer Seegat from that at mesotidal inlets with lower wave energy. Stratigraphic models for tidal-inlet sequences must consider both tide range and wave energy. End_of_Article - Last_Page 759------------