An official website of the United States government
The subspecies rank has been widely applied by taxonomists to capture infraspecific variation within the Linnaean classification system. Many subspecies described throughout the 20th century were recognised largely based on perceived variation in single morphological characters yet have since been found not to correspond to separately evolving population lineages, thus requiring synonymy or elevation to full species under lineage-based views of species. These modern lineage-based taxonomic resolutions have resulted from a combination of new molecular genetic techniques, improved geographical sampling of specimens, and more sophisticated analyses of morphological variation (e.g., statistical assessments rather than solely univariate descriptive ones). Here, we revisit the current taxonomic arrangement of species-level and subspecific taxa in the Lerista microtis (Gray) group, which is distributed along a narrow ~2000 km strip on the southern coast of Australia. From specimens of the L. microtis group, an additional species (Lerista arenicola) and two additional subspecies (L. m. intermedia and L. m. schwaneri) were described. We collected data on mensural, meristic, and colour pattern characters to explore morpho-spatial relationships among these taxa. Although our morphological analyses revealed some distinctiveness among specimens from locations assigned to each taxon, this variation is continuous along Australia’s southern coastline, assuming the form of a geographic cline rather than discrete forms. For many characters, however, spatial patterns were inconsistent with the original descriptions, particularly of the subspecies. Moreover, analysis of genome wide restriction-associated DNA loci revealed multiple instances of paraphyly among taxa, with phylogenetic clustering of specimens assigned to distinct species and subspecies. These emerging patterns provide no support for L. arenicola as a species evolving separately from L. microtis. Additionally, our findings challenge the presumed distinctiveness and coherence of the three subspecies of L. microtis. We thus synonymise L. arenicola and the L. microtis subspecies with L. microtis and provide a redescription of a single yet morphologically variable species—an arrangement that best reflects evolutionary history and the continuous nature of morphological variation across space.
more »
« less
Subspecies at crossroads: the evolutionary significance of genomic and phenotypic variation in a wide-ranging Australian lizard ( Ctenotus pantherinus )
Abstract Many subspecies were described to capture phenotypic variation in wide-ranging taxa, with some later being found to correspond to divergent genetic lineages. We investigate whether currently recognized subspecies correspond to distinctive and coherent evolutionary lineages in the widespread Australian lizard Ctenotus pantherinus based on morphological, mitochondrial and genome-wide nuclear variation. We find weak and inconsistent correspondence between morphological patterns and the presumed subspecies ranges, with character polymorphism within regions and broad morphological overlap across regions. Phylogenetic analyses suggest paraphyly of populations assignable to each subspecies, mitonuclear discordance and little congruence between subspecies ranges and the distribution of inferred clades. Genotypic clustering supports admixture across regions. These results undermine the presumed phenotypic and genotypic coherence and distinctiveness of C. pantherinus subspecies. Based on our findings, we comment on the operational and conceptual shortcomings of morphologically defined subspecies and discuss practical challenges in applying the general notion of subspecies as incompletely separated population lineages. We conclude by highlighting a historical asymmetry that has implications for ecology, evolution and conservation: subspecies proposed in the past are difficult to falsify even in the face of new data that challenge their coherence and distinctiveness, whereas modern researchers appear hesitant to propose new subspecies.
more »
« less
- Award ID(s):
- 1754398
- PAR ID:
- 10373575
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Zoological Journal of the Linnean Society
- Volume:
- 197
- Issue:
- 3
- ISSN:
- 0024-4082
- Format(s):
- Medium: X Size: p. 768-786
- Size(s):
- p. 768-786
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
null (Ed.)The cutthroat trout (Oncorhynchus clarkii (Richardson, 1836)) is one of the most widely distributed species of freshwater fish in western North America. Occupying a diverse range of habitats, they exhibit significant phenotypic variability that is often recognized by intraspecific taxonomy. Recent molecular phylogenies have described phylogenetic diversification across cutthroat trout populations, but no study has provided a range-wide morphological comparison of taxonomic divisions. In this study, we used linear- and geometric-based morphometrics to determine if phylogenetic and subspecies divisions correspond to morphological variation in cutthroat trout, using replicate populations from throughout the geographic range of the species. Our data indicate significant morphological divergence of intraspecific categories in some, but not all, cutthroat trout subspecies. We also compare morphological distance measures with distance measures of mtDNA sequence divergence. DNA sequence divergence was positively correlated with morphological distance measures, indicating that morphologically more similar subspecies have lower sequence divergence in comparison to morphologically distant subspecies. Given these results, integrating both approaches to describing intraspecific variation may be necessary for developing a comprehensive conservation plan in wide-ranging species.more » « less
-
Abstract In a rapidly changing environment, predicting changes in the growth and survival of local populations can inform conservation and management. Plastic responses vary as a result of genetic differentiation within and among species, so accurate rangewide predictions require characterization of genotype-specific reaction norms across the continuum of historic and future climate conditions comprising a species’ range. Natural hybrid zones can give rise to novel recombinant genotypes associated with high phenotypic variability, further increasing the variance of plastic responses within the ranges of the hybridizing species. Experiments that plant replicated genotypes across a range of environments can characterize genotype-specific reaction norms; identify genetic, geographic, and climatic factors affecting variation in climate responses; and make predictions of climate responses across complex genetic and geographic landscapes. The North American hybrid zone ofPopulus trichocarpaandP. balsamiferarepresents a natural system in which reaction norms are likely to vary with underlying genetic variation that has been shaped by climate, geography, and introgression. Here, we leverage a dataset containing 45 clonal genotypes of varying ancestry from this natural hybrid zone, planted across 17 replicated common garden experiments spanning a broad climatic range, including sites warmer than the natural species ranges. Growth and mortality were measured over two years, enabling us to model reaction norms for each genotype across these tested environments. Genomic variation associated with species ancestry and northern/southern regions significantly influenced growth across environments, with genotypic variation in reaction norms reflecting a trade-off between cold tolerance and growth. Using modeled reaction norms for each genotype, we predicted that genotypes with moreP. trichocarpaancestry may gain an advantage under warmer climates. Spatial shifts of the hybrid zone could facilitate the spread of beneficial alleles into novel climates. These results highlight that genotypic variation in responses to temperature will have landscape-level effects.more » « less
-
Meegaskumbura, Madhava (Ed.)The sub-montane East African Reed Frog,Hyperolius substriatusAhl, 1931 (Spotted Reed Frog) has a fragmented highland distribution throughout East Africa. Previous studies show extensive mitochondrial divergence between four lineages of African Spotted Reed Frogs that roughly correspond to previously-recognized subspecies. These may have conservation implications if formally described. However, as mitochondrial-based population models only track maternal patterns, further genomic datasets are necessary to assess the distinctness of these lineages in relation to historically recognized morphological subspecies. In this study, we expanded sampling to newly discovered localities and assessed mitochondrial and genomic data to better understand phylogeography and landscape genomics of this species. We found that genomic clades (biparentally inherited) confirm some of the mitochondrial structure (female inherited), but also revealed multiple cases of mitonuclear discordance particularly within the Udzungwa Mountain block, which may have two separate founding events based on peripatric mitochondrial lineages and panmictic genomic signals. Taken together, the three clades within the geographical range ofH. substriatusthrough Tanzania, Malawi, and Mozambique correspond to three previously-identified subspecies and lineages, and have both spatially cohesive and population-specific patterns of geneflow and isolation with neighboring highland locations.more » « less
-
Rowe, Kevin (Ed.)Abstract The “small-eared” species group of Urocitellus ground squirrels (Sciuridae: Xerinae: Marmotini) is endemic to the Great Basin, United States, and surrounding cold desert ecosystems. Most specific and subspecific lineages in this group occupy narrow geographic ranges, and some are of significant conservation concern; despite this, current taxonomy remains largely based on karyotypic or subtle pelage and morphological characteristics. Here, we leverage 2 multilocus DNA sequence data sets and apply formal species delimitation tests alongside morphometric comparisons to demonstrate that the most widespread small-eared species (U. mollis Kennicott, 1863 sensu lato; Piute Ground Squirrel) is comprised of 2 nonsister and deeply divergent lineages. The 2 lineages are geographically separated by the east-west flowing Snake River in southern Idaho, with no sites of sympatry currently known. Based on robust support across the nuclear genome, we elevate populations previously attributed to U. mollis from north of the Snake River to species status under the name Urocitellus idahoensis (Merriam 1913) and propose the common name “Snake River Plains Ground Squirrel” for this taxon. We delimit 2 subspecies within U. idahoensis; U. i. idahoensis (Merriam 1913) in western Idaho and U. i. artemesiae (Merriam 1913) in eastern Idaho. Urocitellus idahoensis is endemic to Idaho and has a maximal range area of roughly 29,700 km2 spanning 22 counties but occurs discontinuously across this area. Our work substantially expands knowledge of ground squirrel diversity in the northern Great Basin and Columbia Plateau and highlights the difficulty in delimiting aridland mammals whose morphological attributes are highly conserved.more » « less
