The subfamily Acidocerinae

I haven't got to know acidocerines well yet, but there is something intriguing about them, something that calls you to dig deeper in order to get to understand why are they so different (at genus level, at their ecologies and biologies) and yet so (almost frustratingly) similar (at species level- at their external morphology at least).

According to Short & Fikáček (2013), the Acidocerinae are "relatively uniform and difficult to characterize", it is probably due to the fact that members of the subfamily exhibit "an extremely broad range of habitats: many occupy ‘typical’ aquatic habitats such as ponds, marshes, forest pools and stream margins. Some (Agraphydrus, Dieroxenus) are known to occupy hygropetric habitats. Quadriops has never been taken in an aquatic situation and one series was taken from a sap flow in Costa Rica", because as it is expected, different ecologies, may require variations on the structures, which is possibly the reason why you can find so many characters converging along the whole phylogeny.

The subfamily is currently composed by 14 genera and 291 described species:
*In parentheses the number of species per genus

Acidocerus Klug (1)
Agraphydrus Régimbart (37)
Chasmogenus Sharp (43)
Dieroxenus Spangler (1)
Globulosis García (1)
Helobata Bergroth (13)
Helochares Mulsant (180)
Helopeltarium d’Orchymont (1)
Horelophopsis Hansen (2)
Peltochares Régimbart (1)
Quadriops Hansen (6)
Radicitus Short & García (3)
Tobochares Short & García (4)
Troglochares Spangler (1)

In the molecular phylogeny presented by Short & Fikáček (2013), Acidocerinae is the sister clade to the 'Sphaeridiinae lineage' (Rygmodinae+Sphaeridiinae), which is the 'mostly terrestrial group' of hydrophilids. This relationship is strongly supported by the molecular data, but there are currently no morphological synapomorphies for the clade.

(Slightly) Modified from Short & Fikáček (2013).

One of my challenges as an aquatic beetle person would be to find morphological traits that lead to support or question those molecular data.


References

• Hansen, M. (1991). The hydrophiloid beetles. Phylogeny, classification and a revision of the genera (Coleoptera: Hydrophilidae). Biologiske Skrifter, 40, 1–367.

• Short, A. E., & Fikáček, M. (2011). World catalogue of the Hydrophiloidea (Coleoptera): additions and corrections II (2006–2010). Acta Entomologica Musei Nationalis Pragae, 51(1), 83-122.
• Short, A. E. Z., & Fikáček, M. (2013). Molecular phylogeny, evolution and classification of the Hydrophilidae (Coleoptera). Systematic Entomology, 38(4), 723-752.

Hydrophilids to begin

I'm now starting as a Ph.D. student at Kansas University at the Department of Ecology and Evolutionary Biology. I will be working on aquatic beetles systematics, using morphological and molecular data, at the Short Lab.

To be honest, this is my first time working on a group different to broad-nosed weevils, so my knowledge about hydrophilids was very limited until a couple of weeks ago. Two of the things that I know now in general terms of taxonomy are:

- The most influential work on hydrophilids is "The Hydrophiloid Beetles" by Michael Hansen, published in 1991. There he provided, even for genera, diagnoses, descriptions and keys, along with drawings and a phylogenetic analysis. The classification proposed in this publication has been longly used, but a recent molecular analysis published by Andrew Short and Martin Fikáček in 2013, revealed a different configuration ath the subfamily level.

- Not all the so called scavenger water beetles are actually aquatic: of course there are many aquatic species, but there is also a large terrestrial group, and there are also species that occupy intermediate habitats. If you absolutely need to draw a line (and it would not be a straight one... probably would also be diluted), it could be possible to say that the subfamily Sphaeridiinae is mostly composed by terrestrial species and the remaining subfamilies (Hydrophilinae, Chaetarthriinae, Acidocerinae, Rygmodinae and Enochrinae) are represented majorly by aquatic species. These are the subfamilies established on Short & Fikáček's paper.

One of the objectives of my project will be to take a closer look at the morphological characters that grant scavenger water beetles the ability to dive under water, and to see how those characters vary given the different niches that the beetles occupy. In order to tackle this goal, I need to familiarize first with the particular morphology of the group. Fortunately I already have experience with beetle morphology!.

My first aim is to review the genus Helobata (Bergroth, 1888), which has an odd appearance for a hydrophilid... soon I will tell you more about it!


References

• Hansen, M. (1991). The hydrophiloid beetles. Phylogeny, classification and a revision of the genera (Coleoptera: Hydrophilidae). Biologiske Skrifter, 40, 1–367.
• Short, A. E. Z., & Fikáček, M. (2013). Molecular phylogeny, evolution and classification of the Hydrophilidae (Coleoptera). Systematic Entomology, 38(4), 723-752.