Kristenseniscus
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publication ID |
https://doi.org/10.1007/s13127-023-00628-5 |
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persistent identifier |
https://treatment.plazi.org/id/2A7987F0-FFDE-0732-FCCD-FF3DF0D9F97E |
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treatment provided by |
Felipe |
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scientific name |
Kristenseniscus |
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Sympatry of Kristenseniscus View in CoL in the Malay Archipelago
The genus Kristenseniscus has a pantropical/subtropical distribution, but the exact biogeography of its members is yet to be recognised. The oldest described species, K. tessellatus , has confirmed records mainly from the Pacific Ocean basin ( Murray, 1910; Utsugi, 1993; Dastych, 1997a; Claxton, 2004; Li et al., 2008; Suzuki, 2017; see Suzuki et al., 2018 for a summary), reaching Japan in the North, and only two reports from the Indian Ocean basin ( Maucci & Durante Pasa, 1980; Pilato & Binda, 1990; Pilato & Lisi, 2003). In Gąsiorek et al. (2019b) and in the present study, individuals originating from the previously unsurveyed areas, that should be inhabited by this species and incorporated within its geographic range, were studied. The molecular diversity of K. tessellatus specimens from Taiwan, Borneo, Celebes and the Moluccas is low (Fig. 2) and supports the high dispersal potential of this taxon. At the same time, the species is phenotypically very stable and we found no discrepancies between the abovementioned individuals and a Japanese specimen provided by Atsushi Suzuki.
In Gąsiorek et al. (2019b), we signalised problems with the identity of Kristenseniscus limai ( da Cunha & do Nascimento Ribeiro, 1964) by designating it as nomen inquirendum. Although far from being elaborative, the original description does stress the presence of “carination and facetting” in the scapular and caudal (terminal) plates of the African type series, also depicted in a standard way of that time, i.e. neither very detailed nor too general. As it so happens, two years later Schuster and Grigarick (1966), most likely unaware of the Portuguese contribution, described K. kofordi ( Schuster & Grigarick, 1966) from Santa Cruz Island belonging to the Galápagos archipelago, showing in greater detail the dorsal sculpturing as consisting of very large epicuticular granules and ridges forming subplates in the scapular and caudal plates (short epicuticular ridges are present also in the lateralmost portions of paired segmental plates in this species). While studying the former Echiniscus tessellatus group (= Kristenseniscus ), Pilato and Lisi (2003) analysed the Madagascan material collected by Maucci (1993), dissecting three morphotypes that correspond with K. tessellatus , K. kofordi and K. walteri . Beasley and Cleveland (1996), who reported K. limai from the Indomalayan part of China, noted the similarity between K. limai and K. kofordi , but they enumerated alleged differences between the two species: the body size, the cirrus A length and the regularity of dorsal sculpturing. Importantly, K. kofordi is not a larger species according to the present state of knowledge, as Beasley and Cleveland (1996) claimed. da Cunha and do Nascimento Ribeiro (1964) clearly stated that the largest individuals of K. limai attained 142 µm in length, whereas Schuster and Grigarick (1966) determined the body size range of K. kofordi as 120–190 µm. The adult individuals originating from the Sulawesian populations we examined ranged between 130–190 µm (N = 20). We are also sceptical about the presumed disparity in the cirrus A length, as da Cunha and do Nascimento Ribeiro (1964) wrote it measured for 14–15 µm, and Schuster and Grigarick (1966) provided only a value for the holotype (22 µm). Putatively longer cirrus A in K. kofordi may be a derivative of significantly larger body size of a specimen measured (190 µm), as well as a consequence of unreliable morphometric data provided by the authors since Schuster and Grigarick (1966) have already been shown to overestimate measurements of cirrus A in the case of Echiniscus cavagnaroi (Meyer, 2016) . The Sulawesian examples ranged 16–25 µm in this criterion. Finally, the comparison of the “regularity” of sculpturing between the two species seems to be a result of an insufficient sample size being at the disposal of Beasley and Cleveland (1996). Based on the Sulawesian animals, it becomes clear that a species corresponding with the morphotype of K. kofordi ( Figs. 9B View Fig , 14 View Fig and 15 View Fig ) is somehow intermediate in the stability of the development of dorsal sculpturing between very stable and invariant K. tessellatus ( Fig. 9A View Fig ) and a very variable K. walteri ( Figs. 9C View Fig and 10 View Fig ) complex. Especially the lateral epicuticular ridges may be reduced in this species, leading to the morphotype drawn by da Cunha and do Nascimento Ribeiro (1964) as K. limai . In conclusion, in our opinion, there are no morphological differences between K. limai and K. kofordi ; however, a formal status of a junior synonym cannot be assigned to K. kofordi , until new DNA barcodes for Afrotropical and Neotropical populations will confirm or reject this hypothesis. Before this happens, we are inclined to consider K. limai as a pantropical species, with reports from Angola ( da Cunha & do Nascimento Ribeiro, 1964), Venezuela ( Grigarick et al., 1983), Costa Rica ( Kaczmarek & Michalczyk , 2010), Mexico ( Pilato & Lisi, 2006), Colombia ( Lisi et al., 2017), Alabama ( Christenberry, 1979), Florida ( Meyer, 2006), Louisiana ( Hinton & Meyer, 2007), the Galápagos archipelago ( Schuster & Grigarick, 1966), tropical part of China ( Beasley & Cleveland, 1996) and the Malay Archipelago (present study).
Our study revealed at least four species of the walteri complex inhabiting the Malay Archipelago ( K. exanthema sp. nov. and K. cf. walteri 1–3), of which three are characterised with DNA barcodes (Fig. 2). Unfortunately, it is not possible to ascertain whether K. walteri s.s. is present in the Malay Archipelago without molecular data for populations of this species from its terra typica, i.e. Madagascar ( Pilato & Lisi, 2003). However, morphotypes present in the very limited type series (only a holotype and two paratypes) of K. walteri raise concerns whether this species was not described based on specimens representing two different biological species, taking into account that the morphological discrepancies in the Malay examples are minute ( Fig. 10 View Fig ) and that the sculpturing on the scapular plate of the paratype (Fig. 2a in Pilato & Lisi, 2003) is different from that of the holotype (Fig. 2b in Pilato & Lisi, 2003). Moreover, multiple Kristenseniscus species inhabit similar habitats in the Malay Archipelago, and often more than one species is found in the same sample ( Table 1). We hypothesise that the geographic range of K. walteri may be limited to Madagascar. In contrast, K. limai , having a pantropical distribution, is probably the most widespread species in the genus. Furthermore, K. tessellatus exhibits a broad distribution, encompassing the Pacific Ocean basin, but not reaching Afrotropical and Neotropical regions. Thus, the walteri complex seems to have radiated in the Malay Archipelago in sympatry with its congeneric species (the walteri morphotype(s) are unknown for tropical Australia and continental Indomalayan Asia). The evolutionary causes for this phenomenon are yet to be unravelled, but several species living in the same islands and likely nowhere else in the world indicate that this complex may be a weak dispersalist compared with its more distant relatives: K. tessellatus and K. limai . Analogous differentiation in dispersal potential within a complex of relatively close kin has been recently documented for a eutardigrade genus Paramacrobiotus ( Guidetti et al., 2019) . A summary of Kristenseniscus distribution is presented in Fig. 22 View Fig .
The walteri complex clearly represents an advanced state regarding the dorsal sculpturing within the genus: the pseudodivision of plates into subplates shows various stages of reduction (i.e. the return to the uniform, solid plates), reaching completely uniform scapular and caudal plates in K. exanthema sp. nov. Simultaneously, micropores are fully developed and dominate the entire dorsal armour ( Figs. 11 View Fig , 12 View Fig , 13 View Fig ). Lastly, we pinpoint a morphological peculiarity of the entire genus: in specimens with fully extended hind legs, an elongated (dactyloid) papilla IV is apparent ( Figs. 9A View Fig , 11A View Fig , 12A View Fig ). Such a shape of this structure is atypical for the Echiniscus -like genera, which usually exhibit a tubby papilla IV.
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