Field studies in the southeast Asian tropics of northwestern Thailand on the ecomorphological radiation of the rove beetle subfamily Steninae (Coleoptera Staphylinidae)
Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
Final Report Abstract
In order to develop a more comprehensive understanding of the ecological radiation that has occurred in the megadiverse Steninae, ecomorphological studies on this taxon were performed in the Southeast Asian tropics of northern Thailand. During a three months research stay at the entomology lab and collection of the Queen Sirikit Botanic Garden in Chiang Mai, field studies along an elevation gradient in the mountain forests of Doi Inthanon and Doi Pha Hom Pok were performed to evaluate (1) the ecomorphological diversity and (2) the community structure of tropical Steninae. A special interest was to investigate the way that Dianous beetles, lacking a protrudible elongated stick-capture apparatus, capture their prey and interact with characteristic requisites of their habitat. (1) Ecomorphology and evolution: While most trees of our molecular phylogenetic analyses (based on six genes) recovered a monophyletic "Dianous", these (still preliminary) analyses did not yet clearly resolve the basal phylogenetic arrangement of the Steninae including the question of the possible paraphyly of Stenus with respect to Dianous. On the other hand, the view that the enigmatic absence of an elongated protrudable labial prey-capture apparatus in Dianous must be considered a secondary loss that has occurred within Stenus is indirectly supported by our prey-capture experiments. The high mandibular pey-capture success found in Dianous suggests that a specialization in the mandible attack correlates with the elongated labium becoming vestigial and was finally lost as a prey-capture device. Analyses of the critical attack distance and the lateral eye protrusion revealed that these parameters cannot explain this increased prey-capture success, so that the (more falciform) shape of the mandibles found in Dianous beetles and the functional morphology associated with this shape might be the decisive factor here. The strong hygrobiont preferences of these beetles associated with rocks in running waters and waterfalls might support an evolutionary scenario, according to which an adhesive prey-capture apparatus might have become inoperable under wet splashing water conditions and has provoked the improvement of the mandibular prey-capture mechanism. The hygrobiont preference of Dianous beetles is further supported by their tarsal morphology that, in several species, bears especially elongated tape-like setae or a special "tarsal shoe" formed by a dense array of elongated setae. Such structures probably improve the tarsal buoyancy when the beetles plunge onto or actively run on the surface of water. In Dianous, first multivariate approaches describe their differentiation along characters such as eye protrusion, tarsus morphology, antenna and leg length, characters that can be correlated with performance data such as tarsal adhesion. (2) Community structure: 22 Dianous and 60 Stenus species (in total 3148 specimens) were collected across a 2500-m elevational gradient from a variety of habitat types. Among all species collected, six Dianous and one Stenus species were completely new species discoveries and are described for the first time. 18 species recordings were new for Thailand. Increasing Sørensen dissimilarity with increasing elevation was explained by both species turnover (especially across the lower elevational zones) and declining numbers of species (especially across elevations > 1400 m). Unlike the strong decline of the number of species with increasing elevation, species density (i.e., total number of species divided by the number of collection sites at the respective elevational zone) showed a much smoother decline suggesting that the negative gradient in the number of species was superimposed by a land-area effect inherent in mountain shape. In both the litter-inhabiting species and the waterfall-associated species, the numbers of species showed a mid-elevational peak. Species frequency was positively correlated to both elevational (Dianous and Stenus) and habitat niche width (Stenus only). Stenus showed high interspecific variety of wide to narrow niche widths for both elevation and habitat. Numbers of Palearctic and Oriental species deviated from statistical expectation, suggesting that climate niche conservatism has played a role in their elevational distribution. The distributional patterns of Dianous beetles, with their strong hygrobiont preferences associated with rocks in running water and waterfalls, are potentially explained by source–sink dynamics along mountain streams. The described community and distributional patterns presumably have superimposed the overall radiation of Steninae into defined ecomorphs associated with the four major habitat types (i.e., bare ground, litter, vegetation, waterfalls).
Publications
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(2015): Neue und alte Steninen aus Thailand (Coleoptera, Staphylinidae). 342. Beitrag zur Kenntnis der Steninen [New and old Steninae from Thailand (Coleoptera, Staphylinidae). 342th contribution to the knowledge of Steninae]. Linzer biologische Beiträge 47/2:1729-1742
Puthz V.
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(2018): The biology of Steninae, in: Betz, O., Irmler, U. & Klimaszewski, J. (eds.), Biology of rove beetles (Staphylinidae) - Life history, evolution, ecology and distribution, Springer, 229-283
Betz, O., Koerner, L., Dettner, K.
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(2020): Elevational gradients of species richness, community structure, and niche occupation of tropical rove beetles (Coleoptera: Staphylinidae: Steninae) across mountain slopes in Northern Thailand. Evolutionary Ecology, 34:193–216
Betz, O., Srisuka, W., Puthz, V.
