A synopsis of the genus Cylindrostethus Fieber 1861 (Insecta: Hemiptera: Gerridae)

Cylindrostethus Fieber, 1861 is one of the most striking genera of water striders (Insecta: Hemiptera: Gerridae) and has Pantropical distribution. Members of this group can be recognized by the very long, cylindrical body; the short antennomere IV; the short labium not reaching the mesosternum; and by characteristics of the abdomen of males and females. Although Neotropical representatives of the genus have been revised, there are pending taxonomic issues related to this fauna, and that of the Eastern Hemisphere has been barely studied in recent years. Here, we present a short note about the authorship of Cylindrostethus, an updated key to all species of the genus, a new synonymy, and the description of a previously unknown macropterous male of C. hungerfordi Drake and Harris.

Environmental and Seasonal Effects on Gerridae Assemblages (Heteroptera: Gerromorpha) from a Stream in Brazilian Savannah

Our aim here was to assess the seasonal (dry, ebb, and rainy seasons), spatial (upstream, intermediate, and downstream), and environmental effects on the dynamics of Gerridae assemblages (Heteroptera: Gerromorpha) in a Cerrado stream, in central-western Brazil. We sampled the insects on the water line between May 2011 and April 2014 with an 18 cm diameter sieve. We used the scanning method in 100 m of stream in each sampled locality. We sampled 3690 individuals of 19 species. There was a seasonal difference in abundance, which was a result of a lower abundance in the rainy season, but this did not differ between different environments. The estimated species richness was lower upstream and in the rainy season. Species composition was different between the upstream and downstream portions. It was also different among all seasons, with the greatest difference occurring between the rainy and dry seasons. The abiotic factors were responsible for structuring the assemblages in different seasons. The observed differences among seasons in abundance, richness, and species composition have implications for conservation since changes in the structure of the vegetation in the stream edges change the hydrological cycle of streams, and consequently the diversity of the Gerridae assemblages. There was variation in richness and composition between such small distances (upstream and downstream). This shows how sensitive this system can be, and how important elements of the stream's trophic, with the Gerromorpha, can be easily altered.

The genome of the water strider Gerris buenoi reveals expansions of gene repertoires associated with adaptations to life on the water

BACKGROUND

Having conquered water surfaces worldwide, the semi-aquatic bugs occupy ponds, streams, lakes, mangroves, and even open oceans. The diversity of this group has inspired a range of scientific studies from ecology and evolution to developmental genetics and hydrodynamics of fluid locomotion. However, the lack of a representative water strider genome hinders our ability to more thoroughly investigate the molecular mechanisms underlying the processes of adaptation and diversification within this group.

RESULTS

Here we report the sequencing and manual annotation of the Gerris buenoi (G. buenoi) genome; the first water strider genome to be sequenced thus far. The size of the G. buenoi genome is approximately 1,000 Mb, and this sequencing effort has recovered 20,949 predicted protein-coding genes. Manual annotation uncovered a number of local (tandem and proximal) gene duplications and expansions of gene families known for their importance in a variety of processes associated with morphological and physiological adaptations to a water surface lifestyle. These expansions may affect key processes associated with growth, vision, desiccation resistance, detoxification, olfaction and epigenetic regulation. Strikingly, the G. buenoi genome contains three insulin receptors, suggesting key changes in the rewiring and function of the insulin pathway. Other genomic changes affecting with opsin genes may be associated with wavelength sensitivity shifts in opsins, which is likely to be key in facilitating specific adaptations in vision for diverse water habitats.

CONCLUSIONS

Our findings suggest that local gene duplications might have played an important role during the evolution of water striders. Along with these findings, the sequencing of the G. buenoi genome now provides us the opportunity to pursue exciting research opportunities to further understand the genomic underpinnings of traits associated with the extreme body plan and life history of water striders.

Key patterning genes contribute to leg elongation in water striders

BACKGROUND

How adaptive phenotypes are shaped by the action of key developmental genes during ontogeny remains poorly understood. Water striders, a group of hemipteran insects, present a unique example of adaptation to life on the fluid water surface substrate. The group has undergone a set of leg modifications allowing them to efficiently move on the water surface and hence invade a variety of niches from ponds to open oceans. The elongated legs of water striders play a key role in generating efficient movement on the fluid by acting as propelling oars.

RESULTS

To determine the developmental mechanisms underlying leg elongation, we examined the function of the key developmental genes decapentaplegic (dpp), wingless (wg), epidermal growth factor receptor (egfr), and hedgehog (hh) during embryonic development in the water strider Limnoporus dissortis. By analyzing expression patterns and RNAi knockdown phenotypes, we uncover the role of these genes in leg growth and patterning during embryogenesis. Our results indicate that wg and egfr contribute to the elongation of all the three segments of all thoracic legs, whereas hh specifies distal leg segments.

CONCLUSIONS

Together, our results suggest that key patterning genes contribute to the dramatic elongation of thoracic appendages in water striders.