Intraspecific Groups Research Articles

Quantifying interspecific and intraspecific diversity effects on ecosystem functioning.

Rapid environmental changes result in massive biodiversity loss, with detrimental consequences for the functioning of ecosystems. Recent studies suggest that intraspecific diversity can contribute to ecosystem functioning to an extent comparable to contributions of interspecific diversity. Knowledge on the relative importance of these two sources of biodiversity is essential for predicting ecosystem consequences of biodiversity loss and will aid in the prioritization of conservation targets and implementation of management measures. However, our quantitative insights into how interspecific and intraspecific biodiversity loss affects ecosystem functioning and how the effects of these two sources of biodiversity loss on ecosystem functioning can be compared are still very limited. To facilitate such quantitative insights, we extend the interspecific Price partitioning method originally introduced by J. Fox in 2006, previously used to quantify species loss and gain effects on ecosystem functioning, to also account for the effects of intraspecific diversity loss and gain on ecosystem function. Using this extended version can yield the quantitative information required for answering research questions addressing correlations between interspecific and intraspecific diversity effects on ecosystem functioning, identifying interspecific and intraspecific groups with large effects, and assessing whether intraspecific diversity can compensate for losses in interspecific diversity. Applying this method to carefully designed experiments will provide additional insights into how biodiversity loss at different ecological levels contributes to and changes ecosystem functioning.

Incorporating intraspecific variation into species responses reveals both their resilience and vulnerability to future climate change

Incorporating intraspecific variation into species responses can improve our understanding of the effects of climate change. However, most studies overlook such variation or model intraspecific groups independently, leading to widely varying estimates at the species level. In this study, we used a generalized additive framework to model the climate responses of 25 bird species in the tropical Andes, allowing for the estimation of nonlinear responses between subspecies. We measured the effects of environmental covariates (climate, topography, and primary productivity) on relative abundances and projected population trends for near‐future (2050) scenarios. Compared with models that ignored subspecies, the subspecies‐level models performed better in terms of accuracy, discrimination, and goodness‐of‐fit, while projecting fewer species to decline in relative abundance. Thus, species could be more resilient than estimated using species‐level models that ignore intraspecific variation. Nevertheless, our modeling approach also revealed that intraspecific groups may be vulnerable to future threats. We found that subspecies can have low relative abundances and small population sizes. Additionally, based on a preliminary IUCN Red List assessment, one in four subspecies could be threatened due to a small geographical range or a declining population trend. Most of these subspecies at risk inhabit centers of endemism in the northern Andes, such as the Santa Marta Mountains and the Serranía de Perijá. We suggest that protecting subspecies and other intraspecific groups (e.g. populations) could be a critical conservation strategy to buffer against the impacts of climate change, especially in biologically diverse regions.

Regional Characteristics Affecting Distribution of Plain Sculpin Myoxocephalus jaok (Cottidae) in the Russian Territorial Waters in the Sea of Japan

Two intraspecific groups of the plain sculpin Myoxocephalus jaok inhabiting the Russian territoral waters in the Sea of Japan, representing the northern and southern species groups, have been revealed. In a summer season, the species groups are separated from each other by a wide water area extending from 45° to 48° N. The northern species-group nucleus in this period is located in the Tatar Strait inlet, while the southern species group inhabits the Peter the Great Bay. In the summertime, the plain sculpin prefers the upper slope shelf area with water column depths ranged from 80 m (for the southern species group) to 60 m (for the northern species group). The juvenile fish tend to be found in shallower waters as opposed to the mature fish. In a cold season, the majority of fish stocks of the southern species group is still congregating in the Peter the Great Bay, shifting to the shelf edge and the continental slope. Some porton of male fish remains at spawning grounds in the coastal zone to the springtime to guard egg clutches. The specimens of the nothern group leave the shallow-water Tatar Bay inlet at massive level to congregate over the winter in the locations of a deep-water area off the mid-coastal zone of the Sakhalin Island. The specimens of the northern group reach the body length of 67 cm, while the sizes in the southern fish group are larger, reaching 75 cm in length.

Trends in Phenolic Profiles of Achillea millefolium from Different Geographical Gradients.

The traditional widely used raw material of Achillea millefolium is currently mainly derived from wild populations, leading to diversification and uncertainty in its quality. The aim of the study was to determine the accumulation differences of phenolic compounds between geographically distant populations of Achillea millefolium from northern and southern gradients. Plant material was collected from Gaziantep and Nevşehir provinces in Turkey and from wild populations in Lithuania. A complex of nine hydroxycinnamic acids and eleven flavonoids was identified and quantified in the methanolic extracts of inflorescences, leaves, and stems using the HPLC-PDA method. Caffeoylquinic acids predominated in leaves, while inflorescences tended to prevail in flavonoids. The PCA score plot model represented the quantitative distribution pattern of phenolic compounds along a geographical gradient of populations. The content of phenolic compounds in plant materials from northern latitudes was more than twice that of plants from southern latitudes. A significant correlation of individual phenolic compounds with latitude/longitude corresponded to their differences between two countries. Differences in accumulation of caffeoylquinic acids and flavonoids revealed several intraspecific groups within A. millefolium. Our findings suggest that spatial geographical data on the distribution of phenolic compounds in A. millefolium populations could be used as a tool to find potential collection sites for high-quality raw materials.

Similarities in social calls during autumn swarming may facilitate interspecific communication between Myotis bat species

Bats employ a variety of social calls for communication purposes. However, for most species, social calls are far less studied than echolocation calls and their specific function often remains unclear. We investigated the function of in-flight social calls during autumn swarming in front of a large hibernaculum in Northern Germany, whose main inhabitants are two species ofMyotisbats, Natterer’s bats (Myotis nattereri) and Daubenton’s bats (Myotis daubentonii). We recorded social calls in nights of high swarming activity and grouped the calls based on their spectro-temporal structure into ten types and verified our visual classification by a discriminant function analysis. Whenever possible, we subsequently assigned social calls to eitherM. daubentoniiorM. nattereriby analyzing the echolocation calls surrounding them. As many bats echolocate at the same time during swarming, we did not analyze single echolocation calls but the “soundscape” surrounding each social call instead, encompassing not only spectral parameters but also the timbre (vocal “color”) of echolocation calls. Both species employ comparatively similar social call types in a swarming context, even though there are subtle differences in call parameters between species. To additionally gain information about the general function of social calls produced in a swarming context, we performed playback experiments with free-flying bats in the vicinity of the roost, using three different call types from both species, respectively. In three out of six treatments, bat activity (approximated as echolocation call rate) increased during and after stimulus presentation, indicating that bats inspected or approached the playback site. Using a camera trap, we were sometimes able to identify the species of approaching bats. Based on the photos taken during playbacks, we assume one call type to support interspecific communication while another call type works for intraspecific group cohesion.

Genetic diversity and population dynamic of Ziziphus jujuba var. spinosa (Bunge) Hu ex H. F. Chow in Central China.

Phylogeographic research concerning Central China has been rarely conducted. Population genetic and phylogeography of Ziziphus jujuba var. spinosa (also called sour jujube) were investigated to improve our understanding of plant phylogeographic patterns in Central China. Single‐copy nuclear gene markers and complete chloroplast genome data were applied to 328 individuals collected from 21 natural populations of sour jujube in China. Nucleotide variation of sour jujube was relatively high (π = 0.00720, θ w = 0.00925), which resulted from the mating system and complex population dynamics. Analysis of molecular variation analysis revealed that most of the total variation was attributed to variation within populations, and a high level of genetic differentiation among populations was detected (F st = 0.197). Relatively low long‐distance dispersal capability and vitality of pollen contributed to high genetic differentiation among populations. Differences in the environmental conditions and long distance among populations further restricted gene flow. Structure clustering analysis uncovered intraspecific divergence between central and marginal populations. Migrate analysis found a high level of gene flow between these two intraspecific groups. Bayesian skyline plot detected population expansion of these two intraspecific groups. Network and phylogeny analysis of chloroplast haplotypes also found intraspecific divergence, and the divergence time was estimated to occur at about 55.86 Ma. Haplotype native to the Loess Plateau was more ancient, and multiple glacial refugia of sour jujube were found to locate at the Loess Plateau, areas adjacent to the Qinling Mountains and Tianmu Mountains. Species distribution model analysis found a typical contraction‐expansion model corresponding to the Quaternary climatic oscillations. In the future, the distribution of sour jujube may shift to high‐latitude areas. This study provides new insights for phylogeographic research of temperate plant species distributed in Central China and sets a solid foundation for the application of the scientific management strategy of Z. jujuba var. spinosa.

Effects of the analysed variable set composition on the results of distance-based morphometric surveys

Abstract Distance-based morphometry is still widely used in ichthyology. Beside others, this methodology is often used to characterise species or to compare intraspecific group (i.e. population level) differences. However, scarce information is available about: (a) which are the most widely used variables for these purposes, (b) how certain variables are selected for the morphometric analyses, and (c) how variable set compositions and the number of variables affect the results. To answer these questions, a literature review was compiled and our own three datasets were analysed. The results showed that although a high number of variables can be used, previous authors have measured “common” ones most often, regardless of the taxonomic position of the studied group and the goal of the survey. Additionally, our review showed that authors rarely made a variable selection and often did not standardise their datasets; these are methodical problems that make the accuracy and usability of the results questionable. Analyses of our own three datasets showed that the number of variables and the variable set compositions in most cases strongly influenced stock subdivision and the percentage of correctly classified individuals. It was also shown that the most useable variable sets for morphometric purposes can differ considerably depending on the taxon and goal of the survey.

INTRASPECIES POLYMORPHIZM OF GUAR (<i>CYAMOPSIS TETRAGONOLOBA</i> (L.) TAUB.)

In Russia, VIR is the only holder of a collection of guar ( Cyamopsis tetragonoloba (L.) Taub.) – an annual leguminous plant originating from India and Pakistan and used for forage, green manure and as a vegetable. Since after World War II, it got application as an industrial crop. This leguminous plant has a large endosperm with galactomannan providing guar gum. Variability of morphological traits in guar accessions in the VIR collection was evaluated in protected ground conditions of the Pushkin and Pavlovsk Laboratories of VIR in 2017-2019. According to morphological traits description, a method of guar varieties DUS testing was developed. Pod peculiarities provided a basis for differentiating between vegetable and seed/forage guar accessions. The pod size, pod horn length and absence of pubescence were used as the differentiating criteria. On the basis of pod structure, a subdivision of guar into two intraspecific groups, that is the vegetable and grain/forage groups, was suggested. The grain/forage group from Northwestern India and Pakistan demonstrates the traits of wild type, while the vegetable guar has recessive traits, so the former group may be considered as the original one. Dwarf American cultivars represent a separate group of cultivars; yellow-grain cultivars originating from Pakistan and vegetable Australian cultivars from the VIR collection are also distinguished as different morphotypes. A possible intraspecific diversity development of the crop is under discussion.

Social Behavior, Community Composition, Pathogen Strain, and Host Symbionts Influence Fungal Disease Dynamics in Salamanders.

The emerging fungal pathogen, Batrachochytrium dendrobatidis (Bd), which can cause a fatal disease called chytridiomycosis, is implicated in the collapse of hundreds of host amphibian species. We describe chytridiomycosis dynamics in two co-occurring terrestrial salamander species, the Santa Lucia Mountains slender salamander, Batrachoseps luciae, and the arboreal salamander, Aneides lugubris. We (1) conduct a retrospective Bd-infection survey of specimens collected over the last century, (2) estimate present-day Bd infections in wild populations, (3) use generalized linear models (GLM) to identify biotic and abiotic correlates of infection risk, (4) investigate susceptibility of hosts exposed to Bd in laboratory trials, and (5) examine the ability of host skin bacteria to inhibit Bd in culture. Our historical survey of 2,866 specimens revealed that for most of the early 20th century (~1920–1969), Bd was not detected in either species. By the 1990s the proportion of infected specimens was 29 and 17% (B. luciae and A. lugubris, respectively), and in the 2010s it was 10 and 17%. This was similar to the number of infected samples from contemporary populations (2014–2015) at 10 and 18%. We found that both hosts experience signs of chytridiomycosis and suffered high Bd-caused mortality (88 and 71% for B. luciae and A. lugubris, respectively). Our GLM revealed that Bd-infection probability was positively correlated with intraspecific group size and proximity to heterospecifics but not to abiotic factors such as precipitation, minimum temperature, maximum temperature, mean temperature, and elevation, or to the size of the hosts. Finally, we found that both host species contain symbiotic skin-bacteria that inhibit growth of Bd in laboratory trials. Our results provide new evidence consistent with other studies showing a relatively recent Bd invasion of amphibian host populations in western North America and suggest that the spread of the pathogen may be enabled both through conspecific and heterospecific host interactions. Our results suggest that wildlife disease studies should assess host-pathogen dynamics that consider the interactions and effects of multiple hosts, as well as the historical context of pathogen invasion, establishment, and epizootic to enzootic transitions to better understand and predict disease dynamics.

Overlooked Species Diversity and Distribution in the Antarctic Mite Genus Stereotydeus

In the harsh Antarctic terrestrial ecosystems, invertebrates are currently confined to sparse and restricted ice free areas, where they have survived on multi-million-year timescales in refugia. The limited dispersal abilities of these invertebrate species, their specific habitat requirements, and the presence of geographical barriers can drastically reduce gene flow between populations, resulting in high genetic differentiation. On continental Antarctica, mites are one of the most diverse invertebrate groups. Recently, two new species of the free living prostigmatid mite genus Stereotydeus Berlese, 1901 were discovered, bringing the number of Antarctic and sub-Antarctic species of this genus up to 15, of which 7 occur along the coast of Victoria Land and in the Transantarctic Mountains. To examine the biodiversity of Stereotydeus spp., the present study combines phylogenetic, morphological and population genetic data of specimens collected from nine localities in Victoria Land. Genetically distinct intraspecific groups are spatially isolated in northern Victoria Land, while, for other species, the genetic haplogroups more often occur sympatrically in southern Victoria Land. We provide a new distribution map for the Stereotydeus species of Victoria Land, which will assist future decisions in matters of the protection and conservation of the unique Antarctic terrestrial fauna.

Evolutionary biology and interaction among the anastomosis groups of Rhizoctonia spp.

Rhizoctonia solani Kuhn and other Rhizoctonia spp. are the plant pathogenic fungi widespread in the world and in both cultivated and noncultivated soils. Rhizoctonia spp. are readily isolated from diseased plants and soils, which differ in their pathogenicity, cultural, morphological and physiological characteristics. Identification of species and intraspecific groups (ISGs) is sometimes very difficult, due to the absence of the authentic cultures, which hinders mycological and pathological studies. The genus Rhizoctonia can be identified using various techniques such as, sequence analysis of ITS regions, DNA fingerprinting and the rDNA coding sequence. The introduction of the concept of anastomosis groups (AGs) or intraspecific groups has also aided species and subspecies identification. There are 13 different anastomosis groups exists in Rhizoctonia solani of which AG 1-4 were strong pathogenic on many plants and AG 6-10 were orchid mycorrhizae. Analysis of restriction fragment length polymorphisms (RFLPs) and the sequences within ribosomal RNA genes (rDNA) among different anastomosis groups of R. solani isolates exhibited DNA base sequence homology and diverging evolutionary affinities for hyphal anastomosis. More recently, ribosomal DNA (rDNA) sequences have been used to study the genetic relationships between AG of R. solani. The ecology and epidemiology of each ISG of R. solani must be investigated in order to gain a better understanding of this important group of fungi.

Phylogenetic Placement and Phylogeography of Large-Flowered Lotus Species (Leguminosae) Formerly Classified in Dorycnium: Evidence of Pre-Pleistocene Differentiation of Western and Eastern Intraspecific Groups.

The Mediterranean region is a center of species and genetic diversity of many plant groups, which served as a source of recolonization of temperate regions of Eurasia in Holocene. We investigate the evolutionary history of species currently classified in Lotus sect. Bonjeanea in the context of the evolution of the genus Lotus as a whole, using phylogenetic, phylogeographic and dating analyses. Of three species of the section, L. rectus and L. hirsutus have wide Mediterranean distribution while L. strictus has a disjunctive range in Bulgaria, Turkey, Armenia, Eastern Kazakhstan, and adjacent parts of Russia and China. We used entire nuclear ribosomal ITS1-5.8S-ITS2 region (nrITS) and a plastid dataset (rps16 and trnL-F) to reconstruct phylogenetic relationships within Lotus with an extended representation of Bonjeanea group. We analyzed the phylogeographic patterns within each species based on the plastid dataset. For divergence time estimation, the nrITS dataset was analyzed. Our results confirmed the non-monophyletic nature of the section Bonjeanea. They indicate that Lotus is likely to have diverged about 15.87 (9.99–19.81) million years ago (Ma), which is much older than an earlier estimate of ca. 5.54 Ma. Estimated divergence ages within L. strictus, L. rectus, and L. hisrutus (6.1, 4.94, and 4.16 Ma, respectively) well predate the onset of the current type of Mediterranean climate. Our data suggest that relatively ancient geological events and/or climatic changes apparently played roles in early diversification of Lotus and its major clades, as well as in formation of phylogeographic patterns, in at least some species.

Сравнительный анализ изменчивости формы семенных чешуй шишек Larix dahurica и L. cajanderi (Pinaceae)

Сравнительный анализ изменчивости формы семенных чешуй шишек Larix dahurica и L. cajanderi (Pinaceae)

Hybridisation experiments between freshwater prawns Macrobrachium amazonicum and M. pantanalense (Decapoda: Palaemonidae), and the effects of geographical isolation

The freshwater prawns Macrobrachium amazonicum and M. pantanalense are phylogenetically closely related. The present study analysed the occurrence of copulation between these two species. Specimens of M. amazonicum were collected from the Tietê River in Cambaratiba (SP), whereas M. pantanalense specimens were collected from the Lagoa Baíazinha, in Miranda (MS). Six different experimental groups were used, MA♂×MP♀, MA♀×MP♂ (interspecifc), MA♂×MA♀, MP♂×MP♀ (intraspecific), MA♀ and MP♀ (individualised; MA=M. amazonicum and MP=M. pantanalense). The incubation times of the ovigerous females were monitored in all experiments. Some females from all experimental groups were randomly selected and had their oocytes photographed to verify the occurrence of embryonic development. No larvae hatched in the interspecific experimental groups, whereas, in intraspecific groups, almost all experiments (95%) presented larval hatching. The incubation period differed significantly (P<0.001) between the intraspecific groups and all the other experimental groups, but not between each other (P>0.05). The interspecific and individualised groups showed no significant (P>0.05) difference between them. In addition, oocytes from the interspecific experimental groups did not present characteristics of embryonic development. Our results suggest that M. pantanalense and M. amazonicum populations do not copulate, which corroborates the proposal of recent speciation.

The intraspecific structure of the Yellow-spotted ringlet Erebia manto (Denis & Schiffermüller, [1775]), with special reference to the bubastis group: an integration of morphology, allozyme and mtDNA data (Lepidoptera, Nymphalidae, Satyrinae)

Abstract. Present-day intraspecific diversity has largely been shaped by previous climatic events, but the spatial and temporal scales of differentiation processes in most species remain to be clarified. In Europe, the Pleistocene glacial cycles have generated population structures that remain especially evident in montane taxa. The intraspecific variation of the European subalpine Yellow-spotted Ringlet,Erebia manto(Denis & Schiffermüller, [1775]), shows a hierarchical, two-level structure that allows us to study intermediate stages of speciation. Morphologically, three subspecies clusters have been described in this butterfly: themanto,bubastisandvogesiacatype. An allozyme study previously revealed two genetic lineages within themantotype, and two within thevogesiacatype, but lackedbubastisrepresentatives. To further our knowledge of the intraspecific structure ofE. manto, we sampled all known and presumed intraspecific groups and sequenced 1,496 base pairs of the mitochondrial gene COI for 152 specimens from 15 localities. A median joining haplotype network, based on 40 parsimony informative sites, confirmed the four allozyme based lineages. Thebubastistype was acknowledged as a fifth genetic lineage, replacing themantotype populations in the southern part of the western Alps, and separated from it by a well-known zoogeographic borderline. We discuss how the present-day distributions, genetic relationships and timing of the differentiations align.

Why intergroup variation matters for understanding behaviour.

Intergroup variation (IGV) refers to variation between different groups of the same species. While its existence in the behavioural realm has been expected and evidenced, the potential effects of IGV are rarely considered in studies that aim to shed light on the evolutionary origins of human socio-cognition, especially in our closest living relatives—the great apes. Here, by taking chimpanzees as a point of reference, we argue that (i) IGV could plausibly explain inconsistent research findings across numerous topics of inquiry (experimental/behavioural studies on chimpanzees), (ii) understanding the evolutionary origins of behaviour requires an accurate assessment of species' modes of behaving across different socio-ecological contexts, which necessitates a reliable estimation of variation across intraspecific groups, and (iii) IGV in the behavioural realm is increasingly likely to be expected owing to the progressive identification of non-human animal cultures. With these points, and by extrapolating from chimpanzees to generic guidelines, we aim to encourage researchers to explicitly consider IGV as an explanatory variable in future studies attempting to understand the socio-cognitive and evolutionary determinants of behaviour in group-living animals.

Range overlap and spatiotemporal relationships of frugivorous lemurs at Kianjavato, Madagascar

Interspecific competition can strongly influence patterns of space use in animal communities, particularly between closely related species, and may be exacerbated in marginal habitat. This may be important in Madagascar, as lemurs face diminishing resources due to deforestation. We examined the range overlap and spatiotemporal relationships of three species of frugivorous lemur in the fragmented forests of Kianjavato, Madagascar. We conducted simultaneous location and behaviour sampling of black-and-white ruffed lemurs, Varecia variegata , red-fronted lemurs, Eulemur rufifrons , and red-bellied lemurs, Eulemur rubriventer , at two sites over a period of 11 months. We used Doncaster's index of dynamic interaction to investigate the relative amount of time species spent within 30 m and 100 m of each other, compared to the time expected based on random use of location points. All three species showed low core range overlap compared to home range overlap, and while core overlap was higher between interspecific groups than intraspecific groups, the difference was not substantial. Conversely, no spatiotemporal avoidance was observed, and red-fronted lemurs showed positive association (indicating possible attraction) with both red-bellied and ruffed lemurs. These positive spatiotemporal associations may be related to shared resource use in small forests, or predation avoidance strategies. At present, these species may rely more on spatial segregation and niche separation than spatiotemporal avoidance to minimize interspecific competition. • Frugivorous lemurs spatially avoid heterospecifics via low core range overlap. • Spatiotemporally, red-fronted lemurs associate positively with probable competitors. • Positive associations may result from shared limited resources or predators. • Spatial avoidance and niche differentiation may offset spatiotemporal overlap costs.

Do intraspecific life history patterns follow interspecific predictions? A test using latitudinal variation in ringed seals

AbstractMammals adapted to unpredictable and low‐energy environments often evolve a “bet‐hedging” life history strategy characterized by less costly reproductive outputs over a longer and slower‐growing life. In contrast, species adapted to more predictable (i.e., low variation) and higher energy environments may evolve greater fecundity over a shorter and faster‐growing life. We tested whether this known interspecific pattern also occurs within a species. We compared life history traits of the ringed seal (Pusa hispida) in the Canadian High Arctic to those closer to the southern limit of the species' circumpolar distribution. We found that northern seals grew slower than southern seals (Brody growth coefficient), achieved a greater asymptotic body weight (82 and 69 kg vs. 74 and 54 kg female and male, respectively), reached sexual maturity later (6.1 years vs. 4.5 years), had lower fecundity (1.8 years vs. 1.3 years interbirth interval), longer average lifespan (5 years vs. 3 years median age), and greater movements (1,269 vs. 681 km). Mating systems also likely differed with northern seals showing morphological evidence of a promiscuous mating system with potential sperm competition as indicated by greater relative testes size. The northern region was also characterized by more unpredictable environmental timing of seasonal events, such as spring sea ice breakup. Life history variation between the intraspecific groups of seals appears to agree with interspecific patterns and provides a better understanding of how species' life history parameters shift in concert with environmental conditions.

Phenotypic changes in the body of black seabream, Spondyliosoma cantharus (Teleostei: Sparidae), along the eastern Atlantic

Knowledge of population spatial structure is essential in fisheries management. The study of morphological variation patterns in fishes can indicate differences in growth and maturation rates, and thus provide information on group dynamics that should be modelled and managed separately. Identification of intraspecific groups which have different life history features is necessary for understanding population dynamics and achieving a sustainable harvest. The black seabream, Spondyliosoma cantharus, has an extensive distribution along the eastern Atlantic Ocean and is an important commercial fish, exploited in European waters by recreational and commercial fishers. In this paper, body geometric morphometrics was used in order to discriminate among black seabream geographical populations caught in seven different geographical areas. The results showed the existence of intraspecific groups of black seabream across the eastern Atlantic Ocean, with Canary and Angola having clear distinct morphotypes and at least four populations in the European Coast (English Channel, Galicia, Peniche and Algarve) that present stable body shape differences. These populations should be considered to be separate and studies on life history parameters should be enhanced and updated.

Size-dependent variability in the formation and trade-offs of facultative aggregations in golden orb-web spiders (Nephila clavipes)

The vast majority (> 99.99%) of spiders are solitary, but in some species, individuals form stable groups or, alternatively, looser aggregations that fluctuate over space and time. While previous work has documented trade-offs associated with being part of intraspecific groups, rather than being solitary, we know less about why grouping behavior would be facultative. Residing in a group can reduce predation risk, but also lead to competition for food, and we hypothesized that variation in these trade-offs could provide insights into the optional nature of clustering. We used a Costa Rican population of golden orb-web spiders, Nephila clavipes, to ask two questions. First, we tested whether a spider’s size influenced the trade-offs of clustering, and second, whether inter-annual variation in predator and prey abundance could help explain clustering patterns. We also examined the process of cluster formation and dissolution in relation to spider size. Data collected on over 1500 spiders over 4 years indicated that in each year, small spiders experienced the greatest reduction in predation if clustered and also were most likely to initiate aggregations. Overall rates of predation varied significantly among years, and small spiders were most likely to cluster in the year with highest predation. We also detected a cost of clustering in the form of reduced prey capture, but only in years with relatively high overall prey acquisition. Together, these findings suggest that trade-offs that vary individually and over time could influence a spider’s decision to cluster and, hence, explain the facultative nature of aggregating in this population. Animals within a population can show variability in a range of behaviors, such as foraging and predator avoidance, and at times, the ideal way of behaving depends on individual or environmental conditions. In this study, we asked why some female golden orb-web spiders (Nephila clavipes) form groups, while in the same population, others are solitary. This is an interesting question given how rare aggregations are among spiders. In our study, small spiders benefited most from clustering in terms of higher survival when aggregated compared to when solitary. At the same time, spiders of all sizes captured less prey when aggregated, although this cost was only detected in years with relatively abundant prey. Together, these findings suggest that trade-offs that vary individually and over time could influence a spider’s decision to cluster and, hence, explain the optional nature of aggregating in this population.