Stenochrus, Chamberlin, 1922

Monjaraz-Ruedas, Rodrigo, Francke, Oscar F. & Prendini, Lorenzo, 2022, World Travelers: Parthenogenesis and Ecological Tolerance Enable Multiple Colonization Events by the Widespread Short-Tailed Whipscorpion, Stenochrus portoricensis, Insect Systematics and Diversity 6 (1), pp. 1-17 : 11-13

Biogeography of Stenochrus

Stenochrus was estimated to have diverged around 5 Ma (95% HPD: 7.2–3.3 Ma) in southern Mexico. Most diversity in the genus is currently distributed in the mountain ranges of Oaxaca and southern Chiapas, suggesting that the Yucatán Peninsula was subsequently colonized from the mountain ranges of southern Mexico. Southern Mexico was characterized by high volcanic activity during the Miocene and Pliocene (23–2.6 Ma) with the separation of the Isthmus of Tehuantepec serving as an important barrier for faunal dispersal during the Late Miocene ( Mastretta-Yanes et al. 2015), which may have influenced the current distribution and diversity of Stenochrus in this area.

It has been suggested that Pleistocene glaciations played an important role in the current distribution of the Nearctic fauna and flora in Mexico ( Moreno-Letelier and Piñero 2009, Hamilton et al. 2011, Rodríguez-Gómez et al. 2013, Graham et al. 2020, Schramm et al. 2021), a region also considered an important interchange between the Nearctic and Neotropical biotas ( Sanmartín et al. 2001, Devitt 2006, Graham et al. 2020, Schramm et al. 2021). Harveyus Monjaraz-Ruedas et al. 2019 , the putative sister group of Stenochrus is a Nearctic genus distributed in the northern Mexican state of San Luis Potosí, suggesting that Stenochrus could be a Nearctic lineage that dispersed south during the Pleistocene glaciations, as conditions became warmer and drier, and became isolated in refugia such as caves or mountains. Such a scenario might explain the current distribution of Stenochrus in caves along the coast of the Gulf of Mexico and mountain ranges in Oaxaca and Chiapas, as well as its association with the Nearctic fauna, rather than the Mesoamerican fauna as pre - viously believed ( Rowland 1975). As suggested by Monjaraz-Ruedas et al. (2020), some Caribbean schizomid taxa, e.g., Antillostenochrus Armas and Teruel, 2002 , resemble Stenochrus morphologically, suggesting a close relationship. However, the Caribbean schizomid fauna appears to be more closely related to the fauna of South America based on morphology ( Reddell and Cokendolpher 1995, Armas and Abud-Antun 2002, Teruel 2018), suggesting a different evolutionary history in which the Caribbean islands were colonized from South America as suggested for other arachnids ( Esposito et al. 2015,

Esposito and Prendini 2019, Chamberland et al. 2020). A phylogenetic analysis including samples of other Caribbean schizomid genera is needed to test these hypotheses.

Stenochrus portoricensis is abundant in the lowlands of Chiapas, Tabasco, and the Yucatán Peninsula, extending southwards along the coast to the lowlands of Belize, Guatemala, and Honduras. Ancestral area reconstruction suggests it diverged from the MRCA around 1.7 Ma and colonized the lowlands of the Veracruzan Province, on one side, and the Yucatán Peninsula, on the other, explaining the current distributions of the two subclades recovered in the analyses ( Fig. 2 ). The current distribution of the species can be explained by subsequent multiple introductions, from different places, into the Caribbean and other parts of Mexico and Central America.

Text highlighted in boldface indicate best fitting model. LnL, log likelihood;

n, number of free parameters; AIC, Akaike information criterion.

Given the higher genetic diversity within Subclade 2 (see below) and the results of the ancestral area reconstruction, members of Subclade 1 could have been introduced from the lowlands of Chiapas and Tabasco to the Yucatán Peninsula, creating a founder population that initially remained isolated from members of Subclade 2, followed by subsequent introductions from members of Subclade 1 in the Yucatán to the Caribbean, the Pacific coast of Jalisco and Nayarit, and Europe. Such a hypothesis could explain how the species achieved its widespread distribution in such a short time, as well as the low genetic divergence across its distribution.

Figures

Fig. 2. Phylogeographical results for Clade D of the short-tailed whipscorpion, Stenochrus portoricensis Chamberlin, 1922 (Schizomida: Hubbardiidae Cook, 1899). (A, B) Bar plots of results recovered by analyses with BAPS (A) and STRUCTURE (B). (C) Map of North America showing pie charts of individuals with corresponding subclade assignations recovered by analyses with STRUCTURE. (D, E) Median-joining network obtained from Cytochrome c Oxidase Subunit I, COI (D) and Internal Transcribed Spacer, ITS (E): black circles represent median vectors presumed to be unsampled or missing intermediates; hashmarks represent number of mutations between haplotypes;numbers inside circles denote haplotypes;colors denote regions used for ancestral range estimation;circle size proportional to frequencies; dotted line enclosure haplotypes correspond to Subclades 1 and 2 in Fig. 1.