An overview of the sexual dimorphism in Echiniscus (Heterotardigrada, Echiniscoidea), with the description of Echiniscus masculinus sp. nov. (the virginicus complex) from Borneo

Abstract

Members of the genus Echiniscus C.A.S. Schultze, 1840 are mostly unisexual, with thelytokously reproducing females. Therefore, every newly described dioecious species in the genus is particularly interesting. Here, we describe Echiniscus masculinussp. nov. from Gunung Kinabalu, the highest peak of Borneo and the entire Southeast Asia. The new species belongs in the predominantly parthenogenetic E. virginicus complex, and its females are confusingly similar to females of the pantropical E. lineatus Pilato et al., 2008, another member of this group. However, genetic evidence and noticeable sexual dimorphism clearly delineate the new species. Males of E. masculinussp. nov. are unlike females in the body proportions, cuticular sculpturing, and appendage configuration. The new discoveries provide a justification to review the current knowledge about evolution and forms of sexual dimorphism within Echiniscus.

Diversification rates in Tardigrada indicate a decreasing tempo of lineage splitting regardless of reproductive mode

“…The degree of occurrence of parthenogenetic taxa within each group was catagorised based on published literature and anecdotal evidence from colleagues, namely with Echiniscidae assumed to have at least 50% of the species that are able to reproduce sexually (Gąsiorek et al, 2019(Gąsiorek et al, , 2020(Gąsiorek et al, , 2021Piotr Gąsiorek pers. com.…”

“…The selected groups represent two classes distinguished within Tardigrada, the armoured Heterotardigrada Marcus, 1927 andthe soft-bodied Eutardigrada Richters, 1926. The first class is represented by the speciose family Echiniscidae Thulin, 1928 that currently groups about 300 herbivorous species within 21 distinct genera and is characterised by a moderate proportion (about 50%) of parthenogenetic taxa (Gąsiorek et al, 2019(Gąsiorek et al, , 2020(Gąsiorek et al, , 2021Piotr Gąsiorek pers. Com.).…”

An integrative redescription of Echiniscus quadrispinosus quadrispinosus Richters, 1902 (Heterotardigrada, Echiniscidae) from the terra typica in Taunus Mountain Range (Europe; Germany)

“…Echiniscus q. cribrosus and E. q. fissispinosus differ from the nominal species by the absence of 'supplementary plates', which are in fact separated parts of paired plates I and II in E. q. quadrispinosus. Such pseudoplates are often present in other species of Echiniscus (see e.g., Claxton 1996;Kaczmarek & Michalczyk 2010;Claxton & Dastych 2017;Gąsiorek & Kristensen 2018;Bartylak et al 2019;Gąsiorek & Vončina 2019;Gąsiorek & Michalczyk 2020b;Gąsiorek et al 2020;Kiosya et al 2021). Additionally, some differences were also reported in chaetotaxy (e.g., lacking of appendages B, reduced or absent lateral or dorsal appendages).…”

Even one tardigrade is enough. Molecular methods revealed presence of pantropical species <em>Echiniscus lineatus</em> (Heterotardigrada, Echiniscidae) in the fauna of Seychelles

“…Our immature specimen differs from adults (see Pilato, et al, 2008) by complete absence of lateral appendages B (presence or absence of the spine B was also mentioned as polymorphous feature by Gąsiorek, Vončina, and Michalczyk (2020)). Lateral appendages C, D, E have form of thin sharp rigid spines (Fig.…”