Brian K. Lang

The conservation ecology of North American pleurocerid and hydrobiid gastropods

Abstract Many North American freshwater mollusks are at risk of extinction. Knowledge of basic ecology and systematics of the pleurocerid and hydrobiid gastropods is lacking. Pleurocerids are most diverse in southeastern USA, and we know that periphyton food limits their growth, and that their grazing, in turn, limits periphyton biomass. However, we know little about the effects of spates and current velocity on pleurocerid populations, and more work is needed to determine whether interspecific competition or significant risk from predation occurs. Hydrobiids are extremely diverse, but many species inhabit only a few springs (especially in arid western USA) and are at risk of extinction. More work is needed on their population and community ecology. Invasions pose a risk to native snail species. For example, the New Zealand mudsnail (Potamopyrgus antipodarum) interacts negatively with several hydrobiids in the Snake River in western USA. We suggest several research avenues that are needed if we are to maintain and restore pleurocerid and hydrobiid snail populations.

Scale dependence and scale independence in habitat associations of small mammals in southern temperate rainforest

Although field biologists commonly employ methodologies that either are time-tested or are believed (usually for very good reason) to be suitable to the conditions that are encountered, it is rare that results generated using differing methods can be compared on a single fauna. We reanalyze data from three studies conducted on the small mammal fauna of Valdivian temperate rainforests in southern Chile. By restricting our analyses to a relatively homogeneous habitat type we avoid many problems associated with studies over large spatial scales, such as increased species richness via beta diversity. The studies involve a temporal transect, an elevational transect, and a latitudinal transect, and comprise a spatially nested series. Because these studies differed in their initial objectives, they employed different methodologies, both in the field and during subsequent data analysis. At all scales of analysis there is notable overlap in habitat use by all species. Although we observed some seasonal differences in habitat use by species, these were not substantial and involved a small subset of the species. At a local scale, numerically dominant species selected non-random microhabitats but co-occurred with other species more frequently than expected by chance. At a larger spatial scale species appeared to select large subsets of the macrohabitat (i.e., mesohabitat), providing patterns suggestive of apparent competition among species. At an even larger spatial scale, that of temperate southern South America, we predict that species assemblages will again exhibit positive associations. Thus, views on the importance of competition and other biological processes depend critically on the spatial and temporal scales over which observations are made.

A conceptual model linking demography and population genetics of freshwater mussels

Abstract Population viability analysis (PVA) provides a mechanism for analyzing extinction risk by considering processes, such as random fluctuation in demographic features, loss of genetic variation, environmental stochasticity, and the occurrence of catastrophes. Freshwater mussels (Unionoidea) are candidates for PVA because of elevated risk of extinction from anthropogenic activities. We designed a stage-based conceptual model summarizing demographic and genetic changes throughout the mussel life cycle that are associated with changes in population size. We discuss what is known about these stages and the processes that affect transitions between stages. Considerably more information is known about adults than other life stages. Much more work must be done on nonadult life stages because they are potentially vulnerable to disruption via environmental degradation, habitat fragmentation, and loss of vertebrate hosts. New approaches, such as development of molecular identification keys, use of microsatellite markers, and assignment tests to measure dispersal, promise to increase our understanding of nonadult life stages, breeding systems, and linkages among populations. Few studies have attempted to use theory from population biology and conservation genetics to gain insight into strategies for effective conservation. We suggest that more work must be done with species that are not yet critically imperiled because study of such species is likely to yield useful data for PVAs and insight into the mechanisms regulating freshwater mussel populations.

Comparative demography and diversity of small mammals in precordilleran temperate rainforests of Southern Chile

Small mammals were studied in two southern Chilean temperate rainforests in the precor-dillean Andes during 2 low-rainfall years following the 1982 El Nino event. Forests had somewhat different levels of canopy, shrub, and herbaceous cover, and species richness of trees but most of the same plants. Most captures were of four sigmodontine rodents, Akodon olivaceus, Abrothrix longipilis, Abrothrix sanborni , and Oligoryzomys longicaudatus ; five other species and a putative hybrid were recorded. Maximum numbers were in January–July (late summer to winter) and lower numbers in August–December (late winter to early summer). All species had seasonal reproduction in September–April (spring to autumn). A. olivaceus and A. longipilis generally were long-lived, whereas survival rates were low for O. longicaudatus . Responses after the 1982 El Nino were small, and some populations increased during 1984. Populations of A. olivaceus fluctuated more than those of A. longipilis ; those of A. sanborni were low and O. longicaudatus was sporadic and irruptive. Lower-elevational Chilean and precordilleran Argentine forests have similar species composition, but differences in demography and dominance of the former by more widespread, omnivorous A. olivaceus , animalivorous-fungivorous Abrothrix , and granivorous O. longicaudatus . Opportunities for immigration may explain greater homogeneity of populations of small mammals in Chilean rainforests relative to Argentine ones. Although responses to El Nino and subsequent droughts were weak, flowering episodes of bamboo ( Chusquea ) can have strong effects due to increased availability of food.

Past climate change drives current genetic structure of an endangered freshwater mussel species

Historical‐to‐recent climate change and anthropogenic disturbance affect species distributions and genetic structure. The Rio Grande watershed of the United States and Mexico encompasses ecosystems that are intensively exploited, resulting in substantial degradation of aquatic habitats. While significant anthropogenic disturbances in the Rio Grande are recent, inhospitable conditions for freshwater organisms likely existed prior to such disturbances. A combination of anthropogenic and past climate factors may contribute to current distributions of aquatic fauna in the Rio Grande basin. We used mitochondrial DNA and 18 microsatellite loci to infer evolutionary history and genetic structure of an endangered freshwater mussel, Popenaias popeii, throughout the Rio Grande drainage. We estimated spatial connectivity and gene flow across extant populations of P. popeii and used ecological niche models (ENMs) and approximate Bayesian computation (ABC) to infer its evolutionary history during the Pleistocene. structure results recovered regional and local population clusters in the Rio Grande. ENMs predicted drastic reductions in suitable habitat during the last glacial maximum. ABC analyses suggested that regional population structure likely arose in this species during the mid‐to‐late Pleistocene and was followed by a late Pleistocene population bottleneck in New Mexico populations. The local population structure arose relatively recently, perhaps due to anthropogenic factors. Popenaias popeii, one of the few freshwater mussel species native to the Rio Grande basin, is a case study for understanding how both geological and anthropogenic factors shape current population genetic structure. Conservation strategies for this species should account for the fragmented nature of contemporary populations.

REPRODUCTION AND DEVELOPMENT OF Dromiciops gliroides (MARSUPIALIA: MICROBIOTHERIIDAE) IN TEMPERATE RAINFORESTS OF SOUTHERN CHILE

Se describen antecedentes de la biologia reproductiva de Dromiciops gliroides provenientes del analisis de cinco hembras colectadas durante la primavera (octubre - diciembre) de 1984 en el sur de Chile. Se examino el desarrollo morfologico de embriones intrauterinos con analisis microscopico y comparandolos con los atributos morfologicos de ocho juveniles en el marsupio (camadas de diciembre). Los embriones intrauterinos mostraron caracteristicas embrionarias tipicas de neonatos altriciales, quienes migran desde la apertura urogenital hasta el marsupio para completar los ultimos estados del desarrollo. D. gliroides es, aparentemente, una especie monoestrica, estacional, produciendo una camada por ano. Se ha registrado un maximo de cuatro crias, con nacimientos que ocurren en la primavera temprana (octubre). El ciclo de vida de D. gliroides se divide en seis distintos periodos: (a) formacion de pareja, (b) desarrollo intrauterino, (c) paricion, (d) desarrollo intramarsupial, (e) excursiones familiares nocturnas, y (f) independencia juvenil. Las relaciones filogeneticas de D. gliroides con marsupiales del neotropico y Australia son consideradas comparando aspectos de su biologia reproductiva y caracteristicas de su historia de vida temprana

Salinity tolerance as a potential driver of ecological speciation in amphipods (Gammarus spp.) from the northern Chihuahuan Desert

Abstract Ecological speciation is the process by which barriers to gene flow arise between populations as a result of ecologically based divergent selection. Environmental salinity has been identified as one of the most important ecological drivers influencing distribution, abundance, and species richness of aquatic organisms. Springs of the northern Chihuahuan Desert vary in salinity and are home to the Gammarus pecos (Crustacea:Amphipoda) species complex. We used field experiments to compare salinity tolerance among 9 amphipod populations from geographically discrete habitats differing in ambient salinities and to calculate salinity response distances among populations. Cluster analysis placed populations into 3 groups corresponding to low, medium, and high ambient salinities. Partial Mantel tests revealed significant positive correlations between salinity tolerance and habitat salinity after controlling for other variables, such as geographic distance and neutral genetic differences. Our results provide evidence that ecological speciation could be occurring among amphipod populations at different springs, as indicated by dissimilar physiological responses that are correlated with differences in ambient spring salinities. Gene flow is restricted among populations, the restriction is reinforced by dispersal barriers between springs, and selection might preserve variants that most effectively tolerate local salinity levels. Gammarus diversification in the northern Chihuahuan Desert is driven by vicariance and isolation, along with local selection and adaptation.

Genetic and morphologic variation of the Pecos assiminea, an endangered mollusk of the Rio Grande region, United States and Mexico (Caenogastropoda: Rissooidea: Assimineidae)

Assiminea pecos is an endangered species of amphibious gastropod that occupies four widely separated portions of the Rio Grande region in the southwestern United States (Pecos River basin) and northeastern Mexico (Cuatro Cienegas basin). Our statistical and discriminant function analyses of shell variation among the disjunct populations of this species indicate that Mexican specimens differ in their morphometry from those of the United States and can be diagnosed by several characters. We also analyzed variation in the mitochondrial genome by sequencing 658 bp of mitochondrial COI from populations of A. pecos, representatives of the other three North American species of Assiminea, and several outgroups. Our results indicated substantial divergence of the Mexican population of A. pecos, which was consistently depicted as a monophyletic unit nested within or sister to the shallowly structured group comprised of American members of this species. Consistent with our findings, we describe the Mexican population as a new species, which is provisionally placed in the large, worldwide genus Assiminea pending further study of the phylogentic relationships of the North American assimineids. Our molecular data suggest that the Rio Grande region assimineids, which are among the few inland members of the otherwise estuarine subfamily Assimineinae, diverged from coastal progenitors in the late Miocene, with subsequent Pleistocene vicariance of Mexican and American species perhaps associated with development of the modern, lower course of the Rio Grande.

Habitat Associations of the San Bernardino Springsnail, Pyrgulopsis bernardina (Hydrobiidae)

ABSTRACT We studied a critically-endangered hydrobiid snail, Pyrgulopsis bernardina, in Snail Spring, Cochise County, Arizona. We determined the relationships between its abundance and a suite of habitat variables and document formerly-occupied sites. Using Akaikes Information Criterion for model selection and averaging, 14 models were defined a priori using eight habitat variables to explain its abundance. All biologically supported predictors, in the first order, provided the most parsimonious explanation of P. bernardina densities. Structural variables received stronger support than physicochemical variables. P. bernardina densities were positively associated with sand and cobble substrates, vegetation density, water velocity, and dissolved oxygen, as well as water temperatures of 14–22°C and pH values between 7.6 and 8.0. Snail densities were negatively associated with silt and organic substrates, deep water, and high conductance. The current and all former localities for P. bernardina are associated with a shallow aquifer that is distinct from an adjacent deep aquifer.

Taxonomic revision of the Pyrgulopsis gilae (Caenogastropoda, Hydrobiidae) species complex, with descriptions of two new species from the Gila River basin, New Mexico

Abstract We describe two new species of springsnails (genus Pyrgulopsis) for populations from the middle Fork and upper East Fork of the Gila River Basin (New Mexico) that had been previously identified as P. gilae. We also restrict P. gilae to its originally circumscribed geographic range which consists of a short reach of the East Fork Gila River and a single spring along the Gila River (below the East Fork confluence). These three species form genetically distinct lineages that differ from each other by 3.9–6.3% for mtCOI and 3.7–8.7% for mtNDI (the latter data were newly obtained for this study), and are diagnosable by shell and penial characters. Collectively the three species form a strongly supported clade that is distinguished from other congeners by the unique presence of two glandular strips on the dorsal surface of the penial filament. These findings suggest that the conservation status of P. gilae, which was recently removed from the list of candidates for listing as endangered or threatened by the United States Fish and Wildlife Service, should be revisited and that the two new species may also merit protective measures given their narrow geographic ranges.