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| Gambusia nobilis (Baird & Girard 1853) Gambusia pyrros Gambusia echelleorum Portnoy, Bretzing-Tungate, Fields, Bean, Smith, Dolan, Blanchard & Conway, 2025 |
Abstract
Gambusia nobilis is a federally endangered species found across a fragmented distribution within the Pecos River Drainage of Texas and New Mexico, USA. Drought, human water usage, and potential hybridization and competition with introduced congeners threaten species persistence. Therefore, a population genomics study was conducted to provide critical information for conservation planning. Unsupervised clustering suggested hierarchical structure, with a primary K = 3, and deep divergences were detected among samples grouped into the Leon Creek watershed, the Toyah Creek watershed, and water bodies within the Bitter Lake National Wildlife Refuge (F’ST = 0.55–0.76 for putatively neutral data). Phylogenetic analyses showed three distinct clades corresponding to these groups, with divergence times estimated to be in the last 50 000 years. Complimentary morphological analyses detected differences among the three groups, including features of male colour pattern, and the number of caudal-fin rays in both sexes. Taken as a whole, the results indicate that the endangered G. nobilis comprises three species (two of which are named herein as G. pyrros n. sp. and G. echelleorum n. sp.), rather than one, and the study highlights the daunting yet critical task of documenting species diversity during a period of unprecedented diversity loss.
Keywords: Chihuahua desert, genetic drift, taxonomy, Poeciliidae, species delimitation
Subjects:biology, evolution, genomics, taxonomy and systematics
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| Distribution and relationships of the Gambusia nobilis species complex. (a) Map showing distribution of G. nobilis, G. pyrros n. sp. and G. echelleorum n.sp. within Chihuahuan desert ecoregion of western Texas and southeastern New Mexico. (b) Closer view of area surrounded by dashed rectangle (b) in (a), showing location of G. echelleorum samples from Bitter Lake watershed in New Mexio, type locality indicated by black asterisk (*). (c) Closer view of area surrounded by dashed rectangle (c) in (a), showing location of G. nobilis samples from Leon Creek watershed and G. pyrros samples from Toyah Creek watershed in Texas, type localities indicated by black asterisk (*). (d) Clade equivalent to the Gambusia nobilis species complex from the Maximum Likelihood phylogram based on 5989 loci showing relationships of G. nobilis, G. pyrros and G. echelleorum, numbers above branches represent bootstrap values (full topology available in electronic supplementary material, figure S7). (e) Discriminant analysis of principal components using the unsupervised clustering algorithm, K-means (= 3), using 3502 single nucleotide polymorphism-containing loci and 212 individuals (G. nobilis, n = 63; G. pyrros, n = 79; G. echelleorum, n = 70). Basemap in (a) created with SimpleMappr. Satellite images in (b) and (c) obtained from Google Earth. |
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| Male individuals of the three members of the Gambusia nobilis species complex photographed in life against different background and in different views (lateral and dorsal) to document variation in colour pattern. (a) Left side, lateral view, against light grey background: (i) G. nobilis (TCWC 21102.01); (ii, iii) G. pyrros (TCWC 21103.02, paratypes); (iv) G. echelleorum (TCWC 21104.01, holotype); (v-vii) G. echelleorum (TCWC 21105.01, paratypes). (b) Left side, lateral view, against dark grey background: (i, ii) G. nobilis (TCWC 21102.01); (iii) G. pyrros (TCWC 21103.02, paratype); (iv) G. echelleorum (TCWC 21104.01, holotype); (v) G. echelleorum (TCWC 21105.01, paratype). (c) Dorsal view (background variable): (i, ii) G. nobilis (TCWC 21102.01); (iii, iv) G. pyrros (TCWC 21103.02, paratypes); (v) G. echelleorum (TCWC 21104.01, holotype); (vi) G. echelleorum (TCWC 21105.01, paratype |
Gambusia nobilis (Baird & Girard 1853)
Gambusia pyrros new species
Diagnosis: A member of the Gambusia nobilis species group (sensu Rauchenberger [1989]) most similar to G. nobilis and G. echelleorum. The characters distinguishing G. pyrros from G. nobilis are listed in the diagnosis of the latter. Gambusia pyrros is distinguished from G. echelleorum by the same characters that distinguish G. nobilis from G. echelleorum, plus: body colour of males orange-red or yellow-orange (figures 1d and 2b(ii); electronic supplementary material, figure S8) (versus yellow-grey to light cream; figures 1d and 2b(iii); electronic supplementary material, figure S8), anal fin of male orange-red at base in life (figure 2d(ii)) (versus orange; figure 2d(iii)), a higher modal number of total caudal-fin rays (29–32, mode 31 versus 25–29, mode 27; figure 2e), a higher modal number of branched caudal-fin rays (12–15, mode 14 versus 9–14, mode 12).
Etymology: From the Greek pyrros, meaning flame-coloured, a reference to the bright yellow, orange and red colours of the median fins of males in life. A noun in apposition. Proposed common name: flame gambusia.
Gambusia echelleorum new species
Diagnosis: A member of the Gambusia nobilis species group (sensu Rauchenberger [1989]) most similar to G. nobilis and G. pyrros. The characters distinguishing G. echelleorum from G. nobilis and G. pyrros are listed in the diagnoses provided for the latter two.
Etymology: Named for Alice and Anthony Echelle in honour of their work on Gambusia nobilis. A noun in the genitive. Proposed common name: New Mexico Gambusia.
David S. Portnoy; Robert J. Bretzing-Tungate; Andrew T. Fields; Megan G. Bean; Ryan K. Smith; Elizabeth P. Dolan; Rose Blanchard and Kevin W. Conway. 2025. A Total Evidence Approach justifies Taxonomic Splitting of the Endangered Pecos gambusia into Three Species. R Soc Open Sci. (2025) 12 (11): 251025. DOI: doi.org/10.1098/rsos.251025 [26 Nov 2025]
