Contrasting Life History Traits Research Articles

MtDNA data reveal disparate population structures and High Arctic colonization patterns in three intertidal invertebrates with contrasting life history traits

IntroductionPost-glacial climate variation is known to have influenced the distribution of marine species in the North Atlantic. In particular, the Atlantic side of the Arctic has experienced strong fluctuations in both atmospheric and sea surface temperature, as well as seasonal ice coverage since the last glacial maximum (LGM). Here, we aim to unveil the phylogeography and historical demography of three rocky intertidal marine invertebrates showing a trans-Atlantic distribution and presently inhabiting the Arctic: Gammarus oceanicus, Littorina saxatilis and Semibalanus balanoides.MethodsWe used a large amount of mitochondrial DNA barcode data, both newly-obtained and stored in public databases. We performed phylogeographic and demographic analyses on 1119 G. oceanicus, 205 L. saxatilis, and 884 S. balanoides sequences.ResultsOur results show that all three of these boreal species have expanded their effective population sizes in the high Arctic Svalbard Archipelago since the LGM. Analyses investigating the origin of all these populations point to the eastern Atlantic.DiscussionBased on our results we conclude that the expansion of these boreal species to the Arctic possibly happened during an earlier warm cycle of the Holocene era, and is probably not the result of the recent ‘Atlantification’ of the Arctic. We also discuss the effects of dispersal potential on population structure as an important aspect of comparative biogeographical studies.

Highly structured populations of deep-sea copepods associated with hydrothermal vents across the Southwest Pacific, despite contrasting life history traits

Hydrothermal vents are extreme environments, where abundant communities of copepods with contrasting life history traits co-exist along hydrothermal gradients. Here, we discuss how these traits may contribute to the observed differences in molecular diversity and population genetic structure. Samples were collected from vent locations across the globe including active ridges and back-arc basins and compared to existing deep-sea hydrothermal vent and shallow water data, covering a total of 22 vents and 3 non-vent sites. A total of 806 sequences of mtDNA from the Cox1 gene were used to reconstruct the phylogeny, haplotypic relationship and demography within vent endemic copepods (Dirivultidae, Stygiopontius spp.) and non-vent-endemic copepods (Ameiridae, Miraciidae and Laophontidae). A species complex within Stygiopontius lauensis was studied across five pacific back-arc basins at eight hydrothermal vent fields, with cryptic species being restricted to the basins they were sampled from. Copepod populations from the Lau, North Fiji and Woodlark basins are undergoing demographic expansion, possibly linked to an increase in hydrothermal activity in the last 10 kya. Highly structured populations of Amphiascus aff. varians 2 were also observed from the Lau to the Woodlark basins with populations also undergoing expansion. Less abundant harpacticoids exhibit little to no population structure and stable populations. This study suggests that similarities in genetic structure and demography may arise in vent-associated copepods despite having different life history traits. As structured meta-populations may be at risk of local extinction should major anthropogenic impacts, such as deep-sea mining, occur, we highlight the importance of incorporating a trait-based approach to investigate patterns of genetic connectivity and demography, particularly regarding area-based management tools and environmental management plans.

Positive effects of the pollinators Osmia cornuta (Megachilidae) and Lucilia sericata (Calliphoridae) on strawberry quality

In the last decades, the fraction of crops requiring biotic pollination has increased dramatically. While wind- and self-pollination is possible for some of these crops, insect pollination generally increases yields and quality of produce. Especially pollinator communities with varying traits often show additive, positive effects on crop pollination. The aim of this study was to investigate the effect of two pollinator species with contrasting life history traits, the European orchard bee, Osmia cornuta, and the green bottle fly, Luciana sericata, on fruit quality, namely size, weight, shape, and color of fruits of the garden strawberry, Fragaria × ananassa We hypothesized that (1) pollination by both species individually results in higher strawberry quality compared to wind- and self-pollination, and (2) combining both species for pollination leads to higher strawberry quality due to higher functional diversity. To test these hypotheses, we used 40 mesh cages, each containing six strawberry plants. Flowering strawberry plants were either exposed to four O. cornuta individuals, four L. sericata individuals, two individuals of each species, or no pollinators (control) for one week. Fruit weight was only significantly higher than the control treatment when strawberry plants were exposed to bees. Fruit deformation, however, significantly decreased with all three pollinator treatments. Strawberry quality in cages with a combination of bees and flies was not superior to strawberry quality in cages with bees alone. Our results highlight the importance of insect pollination for strawberry quality but increased functional diversity of pollinators did not lead to additive pollination effects.

Wide but not impermeable: Testing the riverine barrier hypothesis for an Amazonian plant species.

Wallace's riverine barrier hypothesis postulates that large rivers, such as the Amazon and its tributaries, reduce or prevent gene flow between populations on opposite banks, leading to allopatry and areas of species endemism occupying interfluvial regions. Several studies have shown that two major tributaries, Rio Branco and Rio Negro, are important barriers to gene flow for birds, amphibians and primates. No botanical studies have considered the potential role of the Rio Branco as a barrier, while a single botanical study has evaluated the Rio Negro as a barrier. We studied an Amazon shrub, Amphirrhox longifolia (A. St.-Hil.) Spreng (Violaceae), as a model to test the riverine barrier hypothesis. Twenty-six populations of A.longifolia were sampled on both banks of the Rio Branco and Rio Negro in the core Amazon Basin. Double-digest RADseq was used to identify 8,010 unlinked SNP markers from the nuclear genome of 156 individuals. Data relating to population structure support the hypothesis that the Rio Negro acted as a significant genetic barrier for A.longifolia. On the other hand, no genetic differentiation was detected among populations spanning the narrower Rio Branco, which is a tributary of the Rio Negro. This study shows that the strength of riverine barriers for Amazon plants is dependent on the width of the river separating populations and species-specific dispersal traits. Future studies of plants with contrasting life history traits will further improve our understanding of the landscape genetics and allopatric speciation history of Amazon plant diversity.

Standardization and Quality Control in Data Collection and Assessment of Threatened Plant Species

Informative data collection is important in the identification and conservation of rare plant species. Data sets generated by many small-scale studies may be integrated into large, distributed databases, and statistical tools are being developed to extract meaningful information from such databases. A diversity of field methodologies may be employed across smaller studies, however, resulting in a lack of standardization and quality control, which makes integration more difficult. Here, we present a case study of the population-level monitoring of two threatened plant species with contrasting life history traits that require different field sampling methodologies: the limestone glade bladderpod, Physaria filiformis, and the western prairie fringed orchid, Plantanthera praeclara. Although different data collection methodologies are necessary for these species based on population sizes and plant morphology, the resulting data allow for similar inferences. Different sample designs may frequently be necessary for rare plant sampling, yet still provide comparable data. Various sources of uncertainty may be associated with data collection (e.g., random sampling error, methodological imprecision, observer error), and should always be quantified if possible and included in data sets, and described in metadata. Ancillary data (e.g., abundance of other plants, physical environment, weather/climate) may be valuable and the most relevant variables may be determined by natural history or empirical studies. Once data are collected, standard operating procedures should be established to prevent errors in data entry. Best practices for data archiving should be followed, and data should be made available for other scientists to use. Efforts to standardize data collection and control data quality, particularly in small-scale field studies, are imperative to future cross-study comparisons, meta-analyses, and systematic reviews.

Contrasting life history and reproductive traits in two populations of Scyliorhinus canicula

The role of natural and sexual selection in generating variability in biological traits between populations represents an intriguing issue in evolutionary biology. Considering their occurrence in different environments and the extensive incidence of post-copulatory sexual selection, elasmobranchs represent an interesting, yet still poorly investigated group. In this study, the life history and reproductive traits of two populations of Scyliorhinus canicula from the northern Adriatic Sea and the Strait of Sicily were compared. Differences in maximum size and size at sexual maturity were observed. The two populations also displayed differences in male and female genitalia. Males in the northern Adriatic Sea presented heavier testes, longer epididymis, seminal vesicles and claspers compared with those in the Strait of Sicily, suggesting the occurrence of stronger sperm competition at the former site. Similarly, females in the northern Adriatic Sea showed heavier oviducal glands and longer reproductive tracts compared with those in the Strait of Sicily. The coevolution between male and female genitalia suggests the occurrence of stronger sexual conflict and/or cryptic female choice in the population from the northern Adriatic Sea. Therefore, natural selection, represented by the different selective pressures occurring at different latitudes, and sexual selection, represented by potentially differing strengths of post-copulatory sexual selection and sexual conflict, may act individually in driving divergence in life history and reproductive traits in these two populations of S. canicula.

The interactions between plant life form and fungal traits of arbuscular mycorrhizal fungi determine the symbiotic community.

Arbuscular mycorrhizal (AM) fungi have traditionally been considered generalist symbionts. However, an increasing number of studies are pointing out the selectivity potential of plant hosts. Plant life form, determined by plant life history traits, seems to drive the AM fungal community composition. The AM fungi also exhibit a wide diversity of functional traits known to be responsible for their distribution in natural ecosystems. However, little is known about the role of plant and fungal traits driving the resultant symbiotic assemblages. With the aim of testing the feedback relationship between plant and fungal traits on the resulting AM fungal community, we inoculated three different plant life forms, i.e. annual herbs, perennial herbs and perennial semi-woody plants, with AM fungal communities sampled in different seasons. We hypothesized that the annual climate variation will induce changes in the mean traits of the AM fungal communities present in the soil throughout the year. Furthermore, the association of plants with different life forms with AM fungi with contrasting life history traits will show certain preferences according to reciprocal traits of the plants and fungi. We found changes in the AM fungal community throughout the year, which were differentially disrupted by disturbance and altered by plant growth form and plant biomass. Both plant and fungal traits clearly contributed to the resultant AM fungal communities. The revealed process can have implications for the functioning of ecosystems since changes in dominant plant life forms or climatic variables could influence the traits of AM fungal communities in soil and hence ecosystem processes.

Fish populations forming transient spawning aggregations: should spawners always be the targets of spatial protection efforts?

Abstract Many coral reef fish form transient spawning aggregations at sites located a few to hundreds of kilometres from their normal residence areas. Reef fish spawning aggregations (“FSAs”) are often heavily exploited, which make them targets for management with marine reserves. We used a per-recruit model to compare the long-term conservation (impacts on female spawning-stock biomass-per-recruit (SSBR) and female : male sex ratio, SR) and fisheries effects (impacts on yield-per-recruit, YPR) of spawning reserves vs. normal residence reserves for two data-poor populations from Seychelles with contrasting life history traits and sexual modes: the Siganus sutor population of the main granitic islands, which has a fast life history and is gonochoristic and the Epinephelus fuscoguttatus population of Farquhar Atoll, which has a slow life history and is protogynous. Overall, our results suggest that normal residence reserves are more effective at improving both the SSBR and YPR of S. sutor. In contrast, the protection of a substantial fraction of spawning sites is preferable for E. fuscoguttatus to ensure the reproductive output of this protogynous population through normalization of SR and maintenance of high SSBR. Neither spawning reserves nor normal residence reserves improved the YPR of E. fuscoguttatus. However, yields of E. fuscoguttatus may increase on the long term via recruitment subsidy if a substantial fraction of spawning sites is protected. This may occur only if the population was recruitment limited in the absence of reserves and increases in SSBR compensate for lost opportunities caused by the area closures. Sensitivity analyses revealed that the relative effects of spawning reserves and normal residence reserves relate more to the change in catchability occurring with FSA formation than to life history traits. Thus, normal residence reserves should be preferred over spawning reserves for S. sutor essentially because its catchability at spawning sites is low relative to many other aggregation-forming populations. S. sutor therefore suffers higher fishing mortality in normal residence areas than at FSA sites. Our study demonstrates that spawning reserves are not always the most effective tool for balancing conservation and exploitation objectives for FSA-forming populations, and that this measure should ideally be weighed against other management options.

Contrasting life history strategies of sympatric Arctic charr morphs, Salvelinus alpinus

In polymorphic populations morphs usually diverge in morphology, ecology and life history, which is most likely driven by adaptations to different environments or resources. Sympatric morphs may develop differences in several life history traits to be able to maximize fitness in alternative niches and habitats. Here, the contrasting life history traits of three sympatric Arctic charr (Salvelinus alpinus (L.)) morphs in a deep and oligotrophic lake in sub-arctic Norway are addressed. The charr morphs differ in spawning habitat and trophic niche. One is a littoral spawning morph that feeds on benthic invertebrates and zooplankton in the littoral and pelagic zones (referred to as the LO-morph), and two other are profundal spawning morphs that either utilize profundal soft bottom benthos as food resource (the PB-morph) or are piscivorous (the PP-morph). The LO-morph typically had intermediate life-history traits relative to the two profundal morphs that had highly contrasting life history traits, especially in growth and age and size of maturity. The PB-morph matured at a young age (∼3 years) and at a small body size (∼8.5 cm), thereby increasing their fitness by investing in reproduction early in life, which results in a short generation time and decreased probability of being predated before first reproduction. The PP-morph on the other hand, matured at an old age (∼9.2 years) and a large body size (∼26 cm), thereby increasing their fitness by investing in somatic growth to enhance initial fecundity, and also to reach a large body size profitable for piscivory. The different trade-off regime between the PP- and PB-morphs seems to be caused by adaptation to alternative trophic niches, and appears to be an important factor for the co-occurrence of the two sister-morphs in the profundal zone.

Contrasting genetic structures of two parasitic nematodes, determined on the basis of neutral microsatellite markers and selected anthelmintic resistance markers

For the first time, the neutral genetic relatedness of natural populations of Trichostrongylid nematodes was investigated in relation to polymorphism of the beta-tubulin gene, which is selected for anthelminthic treatments. The aim of the study was to assess the contribution of several evolutionary processes: migration and genetic drift by neutral genetic markers and selection by anthelminthic treatments on the presence of resistance alleles at beta-tubulin. We studied two nematode species (Teladorsagia circumcincta and Haemonchus contortus) common in temperate climatic zones; these species are characterized by contrasting life history traits. We studied 10 isolated populations of goat nematode parasites: no infected adult goat had been exchanged after the herds were established. Beta-tubulin polymorphism was similar in these two species. One and two beta-tubulin alleles from T. circumcincta and H. contortus respectively were shared by several populations. Most of the beta-tubulin alleles were 'private' alleles. No recombination between alleles was detected in BZ-resistant alleles from T. circumcincta and H. contortus. The T. circumcincta populations have not diverged much since their isolation (F(ST) <0.08), whereas H. contortus displayed marked local genetic differentiation (F(ST) ranging from 0.08 to 0.18). These findings suggest that there are severe bottlenecks in the H. contortus populations, possibly because of their reduced abundance during unfavourable periods and their high reproductive rate, which allows the species to persist even after severe population reduction. Overall, the data reported contradict the hypothesis of the origin of beta-tubulin resistance alleles in these populations from a single mutational event, but two other hypotheses (recurrent mutation generating new alleles in isolated populations and the introduction of existing alleles) emerge as equally likely.

Functional groups of rare plants differ in levels of imperilment

Comparative examination of a large sample of plant species can reveal important aspects of life history that influence the ecology and distribution of taxa and their vulnerability to local extinction. We investigated whether functional groups of 71 rare plant species with contrasting life history traits differed in terms of population losses over time, regional range contraction, and range-wide levels of imperilment. Using town-level occurrence data from herbaria and Natural Heritage Program databases, we characterized species' extents of occurrence as α-hulls encompassing the centroids of New England towns that contained well-documented populations of these rare taxa. Family affiliation was used as a covariate in analyses to reduce phylogenetic bias. Disparate functional groups of plants differed both in proportions of populations lost and declines in range areas over time, with insect-pollinated taxa, upland (vs. wetland) taxa, species with localized seed dispersal modes, and taxa reaching their northern range boundary in New England significantly more imperiled than other functional groups. These techniques permit a broad comparative assessment of the distribution of large numbers of plant taxa, so that we can identify several functional groups that warrant more concerted conservation attention.

The influence of contrasting life history traits and oceanic processes on genetic structuring of rabbitfish populations Siganus argenteus and Siganus fuscescens along the eastern Philippine coasts

Genetic variability and structuring of rabbitfish populations with contrasting life histories, Siganus argenteus and Siganus fuscescens were determined using allozyme analysis. A total of 13–14 polymorphic loci were examined from samples collected in 2002 and 2003 from eight reefs representing 25 populations north (Kuroshio Current) and south (Mindanao Current) of the bifurcation of the North Equatorial Current along the eastern Philippine coast. S. fuscescens populations (H OBS = 0.085) showed higher heterozygosity than S. argenteus (H OBS = 0.053), consistent with predictions of the neutral theory for demersal egg spawners compared to pelagic egg spawners. The generally lower genetic variability of Kuroshio populations may be due to greater environmental disturbance affecting larval mortality and recruitment success. There was no significant overall population genetic structuring for S. argenteus (F ST = 0.01485, P > 0.05) compared to S. fuscescens (F ST = 0.03275, P < 0.05). The latter species showed highly significant genetic structuring among Kuroshio and Mindanao Current populations in both 2002 and 2003 (F CT = 0.08120, P < 0.05; F CT = 0.07500, P < 0.05, respectively), as well as among populations within regions. This conforms to expectations of correlations between observed population genetic structure and life history features related to dispersal potential and gene flow. However, there were significant temporal (i.e., 2002 vs. 2003 samples) genetic variations for both S. fuscescens (F CT = 0.08542, P < 0.05) and S. argenteus (F CT = 0.06330, P < 0.05), which may reflect interannual variability in recruitment success. Differences in population spatial genetic patterns between the two reef fish species suggest that broad scale physical factors (e.g. NEC bifurcation) and regional environmental perturbations (e.g. incidence of typhoons) affect population genetic structure of sympatric congeneric species with different life histories differently. Finer scale ecological processes, which affect larval dispersal and recruitment (e.g., local hydrographic features, distribution of habitats), particularly in the Mindanao Current region, exert more influence on structuring populations of S. fuscescens.

Impact of variable pelagic environments on natural larval growth and recruitment of the reef fish Thalassoma bifasciatum

New recruits of the bluehead wrasse Thalassoma bifasciatum were censused and collected from nearshore reefs of Barbados, West Indies, every 2 weeks for 20 months. Their temporal coincidence with low salinity (&lt;34·5) water during their pelagic larval stage was determined by comparing the otolith records of new recruits with conductivity and temperature records from a current meter moored 2 km off the west coast of the island. Larval residence in a low salinity North Brazil Current (NBC) ring appeared to have a negative impact on growth. Larvae that encountered a NBC ring for at least 7 days during either the first half of the larval period exhibited slower larval growth than those that did not encounter a ring for 7 days during any part of their larval period. As a result of this slower growth, larvae that encountered low salinity waters had a longer pelagic larval duration and were larger at the time of settlement. The magnitude of settlement was not distinctly related to the presence or absence of a NBC ring, but the largest settlement event occurred at the end of the longest ring event. Early juvenile growth did not vary between fish that had encountered a ring and those that did not, so size differences at settlement were propagated through the first week of life on the reef. The potentially opposing attributes of fast and slow‐growing larvae (e.g. fast growing larvae with shorter larval stage duration but smaller size at settlement and higher susceptibility to reef predation), and the resulting differential mortality on the reef may promote the persistence of individuals in the population with contrasting life history traits, and contribute to the lack of a relationship between larval growth and recruitment success. Positive transport related effects of rings (i.e. enhanced retention during some ring events) may further complicate matters by outweighing the negative impact of rings on larval growth.

Fishing effects and life history traits: a case study comparing tropical versus temperate tunas

This study aims to test whether exploitation affects tunas and tuna-like species displaying contrasting life history traits similarly. We first collected information on life history of 10 commercial Atlantic species and then compared this information using multivariate analysis. On one hand, tropical tunas are characterised by small to medium size, rapid growth, early age-at-maturity, long spawning duration and short life span. These species, therefore, display a rapid turnover, characteristic of r-selected species. On the other hand, temperate tunas display differing life history traits, i.e., large size, slow growth, late age-at-maturity, short spawning duration and long life span. The turnover of these species is slow and present characteristics similar to ‘ K-selected’ species (with a conservative strategy adapted to a colder and more variable environment). We, then, selected the two tuna species displaying the most contrasting life histories, i.e., skipjack (SKJ) and bluefin tuna (BFT), and investigated their respective responses to various levels of exploitation, using simulation modelling. If fishing activity starts at age 1 (a situation which is close to the actual exploitation pattern), differences in life history traits make the BFT population much more fragile to exploitation and less productive than SKJ. However, if the fisheries only target adults, both SKJ and BFT populations are able to sustain high F. Spawning stocks and yields of BFT also display conspicuous long-term fluctuations, resulting from the combination of year-to-year variations in the recruitment and a long life span. This variability makes it difficult to detect overfishing or depletion risks in the BFT population. Because of its short life span, SKJ does not display such long-term variations in its SSB. Our simulations also showed that current management measures based on a minimum size limit are much more critical for BFT than SKJ. This difference stresses the importance of taking account of differences in life history traits into management measures.

Oribatid mite biodiversity in agroecosystems: role for bioindication

The general ecology, biology, life history, and available sources for identification of oribatid mites (including Astigmata), the most numerically dominant arachnid group in the organic horizons of most soils, is reviewed. I use this information as the basis to evaluate data on their role for bioindication in agroecosystems, with the following conclusions: (a) oribatid mites with their low metabolic rates, slow development and low fecundity cannot respond rapidly to resource flushes: astigmatic mites with their contrasting life history traits can respond rapidly; (b) because many agroecosystems represent early successional stages, the oribatid species present are those found in heavily disturbed or early successional habitats, wherever these occur; (c) use of oribatid mites for bioindication must incorporate information on life history traits, and habitat and niche profiles for species.

Larval durations and recruitment patterns of two Caribbean gobies (Gobiidae): contrasting early life histories in demersal spawners

Two demersally-spawning fishes were selected to examine the relationship between adult spawning strategies and the early life histories of larvae and juveniles. Although the Caribbean gobies, Coryphopterus glaucofraenum Gill and Gnatholepis thompsoni Jordan are common, co-occurring constituents of nearshore coral reefs, relatively little is known about the early life history and recruitment of their pelagic larvae to the reef environment. To examine patterns of recruitment, recently settled juveniles (7.5 to 16 mm standard length, SL) were censused and collected biweekly from reefs of Barbados, West Indies, during the spring recruitment peak for 3 yr (March to June 1990 to 1992). Otolith analyses were used to determine larval durations and to back-calculate settlement patterns and spawning dates. G. thompsoni spent more than twice as long in the plankton (60 d) than did C. glaucofraenum (27 d). Variation in larval duration of G. thompsoni [coefficient of variation (CV)=22.4%; durations up to 112 d] was significantly greater than that of C. glaucofraenum (CV=9.4%), which suggests that G. thompsoni has a greater capacity for delaying settlement and metamorphosis. Estimated size at settlement for G. thompsoni (SL=8.4 mm) was significantly larger than for C. glaucofraenum (SL=6.4 mm), but post-settlement growth rates were virtually identical (0.21 to 0.22 mm d−1). Settlement of both gobies occurred predominantly around the third quarter moon (ca. Day 21 to 22), but there was much greater spread in the settlement of C. glaucofraenum. Back-calculated spawning frequency for C. glaucofraenum was not closely linked to the lunar cycle, whereas spawning of G. thompsoni occurred more frequently during the third quarter moon. These observations demonstrate that two confamilial demersal spawners may have larvae with contrasting life history traits which can influence patterns of juvenile recruitment. A secondary peak in larval duration of G. thompsoni approximately 1 mo after the major mode (Day 87) suggests that if settlement does not occur two lunar cycles after hatching, G. thompsoni larvae may delay settlement until the following third quarter moon. This coupling suggests that settlement during a particular lunar phase may be advantageous for new recruits, and the capacity to delay metamorphosis may enable tighter synchronization to the lunar cycle.