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ABSTRACT AimThuridillaBergh, 1872, is a lineage of herbivorous sea slugs externally distinguished by bright colours and distinctive patterns of lines and spots. Recent work revealed an exceptionally rapid, cryptic radiation of 13 species in the Indo‐Pacific, raising questions about mechanisms of speciation in this group. Here, we (i) study the diversification and historical biogeography ofThuridillain a phylogenetic context and (ii) assess the role of dispersal and vicariance as the predominant mode of speciation in the genus. LocationTropical and temperate regions of the Atlantic and Indo‐Pacific. Major Taxa StudiesGastropoda, Sacoglossa. MethodsA nearly complete taxon set with 28 out of 32 recognised species ofThuridillawas used, in a total sample of 172 specimens, together with sacoglossan outgroups. Phylogenetic relationships were determined using a multi‐locus approach combining two mitochondrial (COI and 16S) and one nuclear gene (H3). Species relationships, diversification times, and ancestral geographical ranges were inferred using relaxed‐clock methods together with Bayesian discrete phylogeographic methods under three calibration scenarios using the oldest known fossil of Sacoglossa,Berthelinia elegansCrosse, 1875, and tectonic events. ResultsThuridillaspecies branched off into four major clades in all calibration scenarios: two groups from the Atlantic plus Indo‐West Pacific (5 and 6 species) and two clades from the Indo‐West Pacific (4 and 17 species). The highest diversity of the genus is in the Western Pacific (14 spp.) with a peak in the East Indies Triangle (18 spp.), whereas the Atlantic is depauperate with only four species occurring in this ocean basin. Divergence between Atlantic and Indo‐West Pacific lineages occurred in two main temporal periods: the Miocene and the Pliocene. Speciation events within the 13 cryptic species‐complex fell mostly within Plio‐Pleistocene times. Main ConclusionsThe best supported hypothesis was an Indo‐West Pacific origin ofThuridillabetween 28 and 18 Mya during the Early Miocene. In the western Pacific, speciation likely occurred during transient allopatry during Plio‐Pleistocene sea‐level fluctuations. Under the three tested calibration scenarios, the limited diversity of the Atlantic Ocean is hypothesized to be derived from Miocene vicariant events associated with the closure of the Tethys Sea, dispersal across southern Africa, or long‐distance dispersal across the East Pacific Barrier prior to the uplift of the Isthmus of Panama.Thuridillais absent in the Eastern Pacific, potentially resulting from the extinction of ancestral lineages following the uplift of the Isthmus of Panama. Near‐complete sampling of diversity and reconstruction of historical biogeography thus yielded new insight into the relative contributions of dispersal versus vicariance during speciation over the history of this widely distributed, colourful genus.
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Revision of the Indo-West Pacific crab genus Soliella (Brachyura: Xanthidae: Etisinae): ‘pseudocryptic species’ and basinal speciation
Etisine crabs are some of the most abundant cryptobionts in Indo-West Pacific coral reef systems. Despite their ecological importance and abundance in museum collections, several recent systematic studies have indicated family- to subspecies-level taxonomic problems. One such case involves the former chlorodielline genus Soliella Lasley, Klaus & Ng, 2015 (treated here as part of Etisinae), which currently comprises two valid species and three available names that have been in flux in recent literature. The validity of these taxa has only been cursorily discussed. To resolve species limits and distributions, a thorough morphological examination of hundreds of specimens was conducted, including scanning electron microscopy of male gonopods, along with analysis of sequence data of the mitochondrial marker cytochrome c oxidase subunit I (COI) from 84 exemplars across the distribution of the genus. The status of two species that have Indian Ocean versus Pacific Ocean distributions with overlap in the Indo-Australian Archipelago and adjacent regions is confirmed. While external morphology is not reliable for identification, a few discrete, although slight, differences in gonopod morphology were found, and these results are consistent with a “pseudocryptic species” designation. Speciation conforms to a previously published etisine model of allopatric differentiation followed by subsequent divergence of gonopod morphology upon secondary sympatry. This pattern, the biogeography of the two species, and the term “pseudocryptic species” are discussed.
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- Award ID(s):
- 1856245
- PAR ID:
- 10567633
- Publisher / Repository:
- Taylor & Francis
- Date Published:
- Journal Name:
- Systematics and Biodiversity
- Volume:
- 21
- Issue:
- 1
- ISSN:
- 1477-2000
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1080/14772000.2023.2249896
