Amphipod Crustaceans Research Articles

Ecological disturbances and abundance of anthropogenic pollutants in the aquatic ecosystem: Critical review of impact assessment on the aquatic animals

Anthropogenic toxins are discharged into the environment and distributed through a variety of environmental matrices. Trace contaminant detection and analysis has advanced dramatically in recent decades, necessitating further specialized technique development. These pollutants can be mobile and persistent in small amounts in the environment, and ecological receptors will interact with it. Despite the fact that few researches have been undertaken on invertebrate exposure, accumulation, and biological implications, it is apparent that a wide range of pollutants can accumulate in the tissues of aquatic insects, earthworms, amphipod crustaceans, and mollusks. Due to long-term stability during long-distance transit, a number of chemical and microbiological agents that were not previously deemed pollutants have been found in various environmental compartments. The uptake of such pollutants by the aquatic organism is done through the process of bioaccumulation when dangerous compounds accumulate in living beings while biomagnification is the process of a pollutant becoming more hazardous as it moves up the trophic chain. Organic and metal pollution harms animals of every species studied so far, from bacteria to phyla in between. The environmental protection agency says these poisons harm humans as well as a variety of aquatic organisms when the water quality is sacrificed in typical wastewater treatment systems. Contrary to popular belief, treated effluents discharged into aquatic bodies contain considerable levels of Anthropogenic contaminants. This evolution necessitates a more robust and recent advancement in the field of remediation and their techniques to completely discharge the various organic and inorganic contaminants.

Amphipod crustaceans from Chilean Patagonia

This paper describes new or little known Amphipoda collected from Hydrozoa, Bryozoa, Porifera or kelp along the Chilean fjord region. The following species have been found and most of them were redescribed and illustrated: Sunamphitoe femorata (Krøyer, 1845); Caprella cf. equilibra Say, 1818; Haplocheira barbimana robusta K.H. Barnard, 1932; Epimeria (Metepimeria) acanthurus (Schellenberg, 1931); Labriphimedia vespuccii K.H. Barnard, 1931; Leucothoe kawesqari Esquete & Aldea, 2015; Podocerus cf. danae (Stebbing, 1888); Ligulodactylus macrocheir (Schellenberg, 1926) and Torometopa cf. crassicornis (Schellenberg, 1931). One species in this contribution is new to science: Liouvillea rocagloria sp. nov.

Turcogammarus aralensis (Uljanin, 1875), a relict pontogammarid amphipod crustacean from the Aralo-Caspian paleobasin: redescription, phylogenetic position and biogeography

The Ponto-Caspian region harbours the world's second most diverse lacustrine radiation of amphipod crustaceans. The taxonomic position of some of these species is unclear, due to incorrectly defined species limits, poor descriptions, and in some cases, poorly understood characters, such as armament of dorsal integuments. A pertinent example is Turcogammarus aralensis (Uljanin, 1875), which inhabits the Aral Sea and adjacent water bodies like the brackish lake Shalkar (Charkhal), lower reaches of the Syr Darya and Volga, and extends ca. 2500 km westwards in the Black Sea basin. This species has never been properly described, which has led to frequent taxonomic reshuffling. Herein, we provide a full re-description, ascertain its phylogenetic position using the cytochrome c oxidase subunit I (COI) marker, and review its geographical distribution. Our molecular analyses reveal T. aralensis as a sister species to the widespread Obesogammarus crassus (Sars, 1894), and its species status was further confirmed by three molecular species delimitation methods. Turcogammarus aralensis and O. crassus share many similarities such as the setation of the antennae and pereopods 3-4, and poorly setose posterior margin of pereopod 7 basis. Further study is needed to ascertain the validity of the genus Turcogammarus.

Population structure of obligate groundwater amphipod crustaceans (Stygobromus sp.) in alluvial aquifers

Population structure of obligate groundwater amphipod crustaceans (Stygobromus sp.) in alluvial aquifers

Edward Emrys Watkin (1900–1978): marine zoologist and educator

The Welsh marine zoologist, Edward Emrys Watkin (1900–1978), studied the population dynamics of Cardigan Bay herring stocks in the 1920s and subsequently worked on amphipod crustaceans in the Clyde Sea Area in Scotland. His published works span a transitional period in the history of biology, when natural history was being formalized into ecology. A graduate, and a staff member, of the University College of Wales, Aberystwyth, for 45 years he inspired students with his teaching. His experiences as a teacher and examiner were called upon when, in 1965 and 1971, he edited and co-wrote Biology (with Herbert Tisdale Conway and John Brinley Jones), a textbook on biology for pupils seeking the General Certificate of Education (GCE) O-level qualification. However, the impact of Watkins’s book was lessened because of competition from Donald Gordon Mackean’s Introduction to biology published first in 1962.

<i>Corrigendum to</i>: Cryptic diversity down under: defining species in the subterranean amphipod genus <i>Nedsia</i> Barnard & Williams, 1995 (Hadzioidea: Eriopisidae) from the Pilbara, Western Australia

Amphipod crustaceans comprise a significant and enigmatic component of Australian groundwater ecosystems, particularly in the Pilbara region of Western Australia. Many amphipod species in the Pilbara, including species in the genus <i>Nedsia</i> <a href="#R1">Barnard & Williams, 1995</a>, are considered short range endemics, poorly or contentiously defined by taxonomic treatments based on morphology alone and have uncertain distributions as a consequence of this taxonomy. A modern systematic revision of <i>Nedsia</i> is presented here, utilising both molecular and morphological analyses alongside distributional data to delineate species. We describe 13 new species of <i>Nedsia</i>, confirm three existing species and synonymise eight previously described species. <i>Nedsia</i> species are confirmed to be functionally morphologically cryptic, with <i>COI</i> divergences at the 5–20% level. We present comparatively reduced taxonomic descriptions for these cryptic amphipod species in an effort to provide an accelerated pathway for future taxonomic work. The research provides the basis for future environmental impact assessments involving <i>Nedsia</i> species and ongoing monitoring of the groundwater communities these form part of in the resource-rich Pilbara region.

Pilbarana, a new subterranean amphipod genus (Hadzioidea: Eriopisidae) of environmental assessment importance from the Pilbara, Western Australia

The Pilbara and nearby regions in north-western Western Australia have an exceptionally high diversity of short-range endemic invertebrates inhabiting threatened groundwater-dependent habitats. Amphipod crustaceans, in particular, are dominant in these communities, but are poorly understood taxonomically, with many undescribed species. Recent molecular phylogenetic analyses of Pilbara eriopisid amphipods have, nonetheless, uncovered a previously unknown biodiversity. In this study, we formally establish a new genus, Pilbarana Stringer & King gen. nov., and describe two new species, P. grandis Stringer & King sp. nov. from Cane River Conservation Park and P. lowryi Stringer & King sp. nov. from the Fortescue River Basin near the Hamersley Range, using a combination of molecular and morphological data. The new genus is similar morphologically to the two additional Western Australian eriopisid genera, Nedsia Barnard & Williams, 1995 and Norcapensis Bradbury & Williams, 1997, but represents a genetically divergent, reciprocally monophyletic lineage, which can be differentiated by its vermiform body shape, the presence of an antennal sinus, and by the length and form of the antennae and uropods. This research signifies an important contribution to knowledge of Pilbara subterranean communities and has critical implications for future environmental impact assessments and conservation management.

Global distribution and diversity of alien Ponto-Caspian amphipods

The Ponto-Caspian region is an important donor of aquatic alien species throughout the Northern Hemisphere, many of which are amphipod crustaceans. Despite decades of ongoing spread and negative effects on native biota, a complete picture of the global diversity and distribution of these amphipods has yet to emerge, hampering efficient monitoring and predictions of future invasion pathways. Herein, we provide a comprehensive summary of alien species taxonomic and ecomorphological diversity, as well as high-resolution distribution maps and biogeographical patterns based on > 8000 global records. We find that up to 39 species in 19 genera and five families, belonging to all four currently recognized ecomorphs, are potentially alien, their diversity gradually decreasing with distance from the native region. Most species (62%) have limited distributions, 15% are widespread, and 23% exhibit intermediate ranges. We also find that regions adjacent to the native range are comparatively less well-sampled than more distant regions. Biogeographical clustering revealed three faunal provinces that largely correspond with the Southern, Central and Northern invasion corridors. We conclude that (1) alien amphipods are a representative subsample of the native Ponto-Caspian phylogenetic and ecomorphological diversity, and (2) that their biogeographical patterns are driven by anthropogenic factors acting on taxonomically distinct native regional species pools.

Would Antarctic Marine Benthos Survive Alien Species Invasions? What Chemical Ecology May Tell Us

Many Antarctic marine benthic macroinvertebrates are chemically protected against predation by marine natural products of different types. Antarctic potential predators mostly include sea stars (macropredators) and amphipod crustaceans (micropredators) living in the same areas (sympatric). Recently, alien species (allopatric) have been reported to reach the Antarctic coasts, while deep-water crabs are suggested to be more often present in shallower waters. We decided to investigate the effect of the chemical defenses of 29 representative Antarctic marine benthic macroinvertebrates from seven different phyla against predation by using non-native allopatric generalist predators as a proxy for potential alien species. The Antarctic species tested included 14 Porifera, two Cnidaria, two Annelida, one Nemertea, two Bryozooa, three Echinodermata, and five Chordata (Tunicata). Most of these Antarctic marine benthic macroinvertebrates were chemically protected against an allopatric generalist amphipod but not against an allopatric generalist crab from temperate waters. Therefore, both a possible recolonization of large crabs from deep waters or an invasion of non-native generalist crab species could potentially alter the fundamental nature of these communities forever since chemical defenses would not be effective against them. This, together with the increasing temperatures that elevate the probability of alien species surviving, is a huge threat to Antarctic marine benthos.

Two new species add to the diversity of Eoniphargus in subterranean waters of Japan, with molecular phylogeny of the family Mesogammaridae (Crustacea, Amphipoda)

Amphipod crustaceans are a major group of invertebrates that predominantly occur in groundwater ecosystems. Eoniphargus is a mesogammarid genus with only two known species from the groundwater systems of the Japanese archipelago and Korean Peninsula. However, there is a dearth of taxonomic studies on this genus, and the species diversity within Eoniphargus is unclear. Here, we describe two new species, E. iwataorumsp. nov. and E. toriiisp. nov., collected from the interstitial waters in Tochigi and Shizuoka Prefectures in the Japanese archipelago. These two new species are distinguished from their congeners by the following features: head, urosomite 3, first and second antennae, mandibles, and maxilla 1. Eoniphargus kojimai is redescribed here based on material collected near the type locality. Molecular phylogenetic analyses based on the nuclear 28S rRNA and mitochondrial COI genes revealed that E. kojimai is sister to E. iwataorumsp. nov. In this study, we also briefly discuss the phylogenetic relationships of Mesogammaridae based on the molecular phylogenetic analyses.

Low-frequency noise pollution impairs burrowing activities of marine benthic invertebrates

Sounds from human activities such as shipping and seismic surveys have been progressively invading natural soundscapes and pervading oceanic ambient sounds for decades. Benthic invertebrates are important ecosystem engineers that continually rework the sediment they live in. Here, we tested how low-frequency noise (LFN), a significant component of noise pollution, affects the sediment reworking activities of selected macrobenthic invertebrates. In a controlled laboratory setup, the effects of acute LFN exposure on the behavior of three abundant bioturbators on the North Atlantic coasts were explored for the first time by tracking their sediment reworking and bioirrigation activities in noisy and control environments via luminophore and sodium bromide (NaBr) tracers, respectively. The amphipod crustacean Corophium volutator was negatively affected by LFN, exhibiting lower bioturbation rates and shallower luminophore burial depths compared to controls. The effect of LFN on the polychaete Arenicola marina and the bivalve Limecola balthica remained inconclusive, although A. marina displayed greater variability in bioirrigation rates when exposed to LFN. Furthermore, a potential stress response was observed in L. balthica that could reduce bioturbation potential. Benthic macroinvertebrates may be in jeopardy along with the crucial ecosystem-maintaining services they provide. More research is urgently needed to understand, predict, and manage the impacts of anthropogenic noise pollution on marine fauna and their associated ecosystems.

The roles of landscape of fear and light in allowing the exploitation of spring habitats by subterranean amphipods: an experimental and field approach

Border habitats such as interfaces and ecotones promise research targets from an evolutionary and zoological point of view. Springs are typical ecotones that border two strongly distinct environments: surface and underground. They are exploited by both subterranean and surface species for which they may provide specific environmental pressures promoting phenotypic plasticity and local adaptations. The aim of this study is to understand how the landscape of fear (LOF) and physical constraints, like light occurrence, affect springs' exploitation by both a subterranean (Niphargus thuringius) and a surface crustacean amphipod species (Echinogammarus stammeri). From March to May 2021, we surveyed 15 springs, divided into 25 plots according to their distance to the border, and both day and night, we recorded amphipods activity and LOF levels for them. In a subterranean laboratory, we also reared 80 N. thuringius and 80 E. stammeri in safe and risky conditions with constant darkness and diel light variation assessing their activity and survival for 30 days. Risky conditions were represented by meso-predators (four fire salamander larvae) alone or with a top-predator (a dragonfly larva of the species Cordulegaster boltonii). While in field conditions, the activity of N. thuringius seemed negatively affected by the number of active predators, in laboratory experiments, the main role was played by the light treatment; activity was significantly higher in constant darkness conditions. E. stammeri activity in the field was higher in surface plots, while in laboratory conditions was affected by LOF. Predation risk negatively affected the survival of both amphipods. Our findings reveal that while light conditions seem to shape activity patterns of stygobionts strongly, predators have a lower effect on activity, even though predators have negative effects on survival. Moreover, physical constraints, such as light exposure, can affect antipredator responses of subterranean organisms, thus representing selective pressures for the exploitation of surface environments.

Identification and classification of cis-regulatory elements in the amphipod crustacean Parhyale hawaiensis.

Emerging research organisms enable the study of biology that cannot be addressed using classical 'model' organisms. New data resources can accelerate research in such animals. Here, we present new functional genomic resources for the amphipod crustacean Parhyale hawaiensis, facilitating the exploration of gene regulatory evolution using this emerging research organism. We use Omni-ATAC-seq to identify accessible chromatin genome-wide across a broad time course of Parhyale embryonic development. This time course encompasses many major morphological events, including segmentation, body regionalization, gut morphogenesis and limb development. In addition, we use short- and long-read RNA-seq to generate an improved Parhyale genome annotation, enabling deeper classification of identified regulatory elements. We discover differential accessibility, predict nucleosome positioning, infer transcription factor binding, cluster peaks based on accessibility dynamics, classify biological functions and correlate gene expression with accessibility. Using a Minos transposase reporter system, we demonstrate the potential to identify novel regulatory elements using this approach. This work provides a platform for the identification of novel developmental regulatory elements in Parhyale, and offers a framework for performing such experiments in other emerging research organisms.

Regulation of gene expression during ontogeny of physiological function in the brackishwater amphipod Gammarus chevreuxi.

Embryonic development is a complex process involving the co-ordinated onset and integration of multiple morphological features and physiological functions. While the molecular basis of morphological development in embryos is relatively well known for traditional model species, the molecular underpinning of the development of physiological functions is not. Here, we used global gene expression profiling to investigate the transcriptional changes associated with the development of morphological and physiological function in the amphipod crustacean Gammarus chevreuxi. We compared the transcriptomes at three timepoints during the latter half of development, characterised by different stages of the development of heart form and function: 10days post fertilisation (dpf, Early: no heart structure visible), 15 dpf (Middle: heart present but not fully functional), and 18 dpf (Late: regular heartbeat). Gene expression profiles differed markedly between developmental stages, likely representing a change in the activity of different processes throughout the latter period of G. chevreuxi embryonic development. Differentially expressed genes belonged to one of three distinct clusters based on their expression patterns across development. One of these clusters, which included key genes relating to cardiac contractile machinery and calcium handling, displayed a pattern of sequential up-regulation throughout the developmental period studied. Further analyses of these transcripts could reveal genes that may influence the onset of a regular heartbeat. We also identified morphological and physiological processes that may occur alongside heart development, such as development of digestive caeca and the cuticle. Elucidating the mechanisms underpinning morphological and physiological development of non-model organisms will support improved understanding of conserved mechanisms, addressing the current phylogenetic gap between relatively well known model species.

Individual small in-stream barriers contribute little to strong local population genetic structure five strictly aquatic macroinvertebrate taxa.

Water flow in river networks is frequently regulated by man‐made in‐stream barriers. These obstacles can hinder dispersal of aquatic organisms and isolate populations leading to the loss of genetic diversity. Although millions of small in‐stream barriers exist worldwide, their impact on dispersal of macroinvertebrates remains unclear. Therefore, we, therefore, assessed the effects of such barriers on the population structure and effective dispersal of five macroinvertebrate species with strictly aquatic life cycles: the amphipod crustacean Gammarus fossarum (clade 11), three snail species of the Ancylus fluviatilis species complex and the flatworm Dugesia gonocephala. We studied populations at nine weirs and eight culverts (3 pipes, 5 tunnels), built 33–109 years ago, mainly in the heavily fragmented catchment of the river Ruhr (Sauerland, Germany). To assess fragmentation and barrier effects, we generated genome‐wide SNP data using ddRAD sequencing and evaluated clustering, differentiation between populations up‐ and downstream of each barrier and effective migration rates among sites and across barriers. Additionally, we applied population genomic simulations to assess expected differentiation patterns under different gene flow scenarios. Our data show that populations of all species are highly isolated at regional and local scales within few kilometers. While the regional population structure likely results from historical processes, the strong local differentiation suggests that contemporary dispersal barriers exist. However, we identified significant barrier effects only for pipes (for A. fluviatilis II and III) and few larger weirs (>1.3 m; for D. gonocephala). Therefore, our data suggest that most small in‐stream barriers can probably be overcome by all studied taxa frequently enough to prevent fragmentation. However, it remains to be tested if the strong local differentiation is a result of a cumulative effect of small barriers, or if larger in‐stream barriers, land use, chemical pollution, urbanization, or a combination of these factors impede gene flow.

Diversity and Zonation of Benthic Amphipod Crustaceans Affected by the Mississippi Submarine Canyon in the Northern Gulf of Mexico

Amphipod crustacean diversity and zonation are described from the large Mississippi Canyon that extends from the continental shelf across the entire continental margin. Benthic amphipods were sampled on four cruises from 2000 to 2004 from six locations in the Mississippi Canyon from depths of 480 through 2,750 m, and compared with five locations in a second transect on the open continental slope approximately 100 km west of the canyon to assess the canyon effect on the structure and composition of amphipod assemblages. Five replicates were collected from each location using 0.2 m–2 GOMEX box corer. Amphipods amounted to 40% of the total faunal abundance within the canyon compared to only 4% in the non-canyon samples. Of the seventy-two species (19 families) collected, 61 were encountered in the canyon compared to 38 on the non-canyon transect. The trough-like head of the canyon (480 m) supported high densities (4,446–26,933 ind./m2) of the filter feeding, tube dwelling ampeliscid amphipod (Ampelisca mississippiana), the highest densities sampled compared to any other single species, at any other location, either within or outside the canyon, reflecting extreme flux of organic detritus from the continental shelf. The dominance by this single species suppressed the within – habitat (alpha) diversity and evenness, compared to relatively high diversity within the 1,000–1,500 m depths interval both in and outside the canyon. The species richness and alpha diversity exhibited mid-depth maxima at ca. 1,100 m both in and out of the canyon. High species richness (61) over the entire length of the canyon is presumed to be a function of greater topographic complexity and intermittent mass wasting of sediment down the canyon axis. The absence of nestedness is attributed to the amphipod reproductive pattern that lacks dispersive larval stages and brooding comparatively small numbers of eggs in this taxon. Despite depressed diversity at the head of the canyon, the fact that the number of amphipod species in the Mississippi Canyon was 1.5 times their numbers on the adjacent slope suggests that this physiographic feature enriches geographic-scale species diversity.

Invader abundance and contraction of niche breadth during replacement of a native gammarid amphipod.

The introduction of non‐native species to new locations is a growing global phenomenon with major negative effects on native species and biodiversity. Such introductions potentially bring competitors into contact leading to partial or total species replacements. This creates an opportunity to study novel species interactions as they occur, with the potential to address the strength of inter‐ and intraspecific interactions, most notably competition. Such potential has often not been realized, however, due to the difficulties inherent in detecting rapid and spatially expansive species interactions under natural field conditions. The invasive amphipod crustacean Gammarus pulex has replaced a native species, Gammarus duebeni celticus, in river and lake systems across Europe. This replacement process is at least partially driven by differential parasitism, cannibalism, and intraguild predation, but the role of interspecific competition has yet to be resolved. Here, we examine how abundance of an invasive species may affect spatial niche breadth of a native congeneric species. We base our analyses of niche breadth on ordination and factor analysis of biological community and physical parameters, respectively, constituting a summative, multidimensional approach to niche breadth along environmental gradients. Results derived from biological and environmental niche criteria were consistent, although interspecific effects were stronger using the biological niche approach. We show that the niche breadth of the native species is constrained as abundance of the invader increases, but the converse effect does not occur. We conclude that the interaction between invasive G. pulex and native G. d. celticus under natural conditions is consistent with strong interspecific competition whereby a native, weaker competitor is replaced by a superior invasive competitor. This study indicates a strong role of interspecific competition, alongside other known interactions such as differential intraguild predation, in rapid and expansive species replacements following biological invasions.

Cryptic diversity down under: defining species in the subterranean amphipod genus

Amphipod crustaceans comprise a significant and enigmatic component of Australian groundwater ecosystems, particularly in the Pilbara region of Western Australia. Many amphipod species in the Pilbara, including species in the genus Nedsia Barnard & Williams, 1995, are considered short range endemics, poorly or contentiously defined by taxonomic treatments based on morphology alone and have uncertain distributions as a consequence of this taxonomy. A modern systematic revision of Nedsia is presented here, utilising both molecular and morphological analyses alongside distributional data to delineate species. We describe 13 new species of Nedsia, confirm three existing species and synonymise eight previously described species. Nedsia species are confirmed to be functionally morphologically cryptic, with COI divergences at the 5–20% level. We present comparatively reduced taxonomic descriptions for these cryptic amphipod species in an effort to provide an accelerated pathway for future taxonomic work. The research provides the basis for future environmental impact assessments involving Nedsia species and ongoing monitoring of the groundwater communities these form part of in the resource-rich Pilbara region.

First Glimpse at the Diverse Aquaporins of Amphipod Crustaceans.

The importance of aquaporins (AQPs) in the transport of water and solutes through cell membranes is well recognized despite being relatively new. To date, despite their abundance, diversity, and presence in disparate environments, amphipods have only been mentioned in studies about the AQPs of other animals and have never been further investigated. In this work, we aimed to recover from public data available AQPs of these crustaceans and reconstruct phylogenetic affinities. We first performed BLAST searches with several queries of diverse taxa against different NCBI databases. Then, we selected the clades of AQPs retrieving the amphipod superfamily Gammaroidea as monophyletic and ran phylogenetic analyses to assess their performances. Our results show how most of the AQPs of amphipods are similar to those of other crustaceans, despite the Prip-like displayed different paralogs, and report for the first time a putative Aqp8-like for arthropods. We also found that the candidate genes of Prip-like, Bib-like, Aqp12-like, and Glp-like help solve deeper relationships in phylogenies of amphipods while leaving uncertainties in shallower parts. With our findings, we hope to increase attention to the study of amphipods as models for AQP functioning and evolution.

Ancient volcanos as species pumps: A case study of freshwater amphipods in Northeast Asia.

Volcano-tectonic processes have been viewed as primary drivers in the formation of present-day diversity. Volcanos associated with mountain uplifts drive allopatric speciation through vicariance and may impact the surrounding areas like species pump or species attractor. However, the application of these hypotheses to aquatic fauna has rarely been tested explicitly. We tested these hypotheses in the Changbai Mountains (Mts), which are one of the most typical, active volcanic ranges in Northeast (NE) Asia with a long and turbulent geological history. The Gammarus nekkensis species complex of amphipod crustaceans, widely distributed throughout NE Asia with poor dispersal abilities and a long evolutionary history, is a suitable model for testing hypotheses of species pump or species attractor. Phylogenetic and ancestral range reconstructions demonstrated that the studied amphipod originated from the Changbai Mts ~27Ma and diverged into eastern (Clade I) and western (Clade II) clades, which corresponds well with the initial volcanic eruption of the Changbai Mts in the Late Oligocene. The subsequent diversifications of subclades CI-3, CII-1a and CII-2a were probably driven by second and third eruptions of the Changbai Mts during the Miocene. In particular, the Changbai lineages had spread to the Russian Far East multiple times since the Early Miocene, and widely colonized the region during the Pleistocene. Our discoveries suggest that the ancient volcanos of the Changbai Mts act as species pumps in NE Asia, resulted in burst of diversification around the Changbai Mts and subsequent dispersals into adjacent regions.