The evolution of water balance inGlossina(Diptera: Glossinidae): correlations with climate

Abstract

The water balance of tsetse flies (Diptera: Glossinidae) has significant implications for understanding biogeography and climate change responses in these African disease vectors. Although moisture is important for tsetse population dynamics, evolutionary responses of Glossina water balance to climate have been relatively poorly explored and earlier studies may have been confounded by several factors. Here, using a physiological and GIS climate database, we investigate potential interspecific relationships between traits of water balance and climate. We do so in conventional and phylogenetically independent approaches for both adults and pupae. Results showed that water loss rates ( WLR) were significantly positively related to precipitation in pupae even after phylogenetic adjustment. Adults showed no physiology-climate correlations. Ancestral trait reconstruction suggests that a reduction in WLR and increased size probably evolved from an intermediate ancestral state and may have facilitated survival in xeric environments. The results of this study therefore suggest an important role for water balance physiology of pupae in determining interspecific variation and lend support to conclusions reached by early studies of tsetse physiology.

Phenotypic plasticity of desiccation resistance inGlossinapuparia: are there ecotype constraints on acclimation responses?

“…The magnitude of intraspecific variation in desiccation resistance induced by the acclimation treatments in these laboratory‐reared species was substantial (a minimum of 15× range of variation within G. pallidipes and a maximum of 25× variation in G. austeni ). Indeed, comparison with our previous study of inter‐specific variation in pupal WLR (Kleynhans & Terblanche, 2009) suggests that variation in desiccation resistance among species may be obscured by the magnitude of phenotypic plasticity, particularly for similar‐sized species. This could be a significant problem when undertaking species comparisons (e.g.…”

“…2). Xeric or mesic classification was assigned according to the combined environmental mean annual precipitation and mean annual temperature (Bursell, 1959;Kleynhans & Terblanche, 2009). This experimental design was employed to assess possible constraints on acclimation responses based on phylogenetic or ecotype (xeric ⁄ mesic) association.…”

“…hot and dry) when it is least efficient to forage (see Terblanche & Chown, 2007). Indeed, it has been well demonstrated that Glossina species have evolved desiccation resistance to match local climate conditions in the pupal stage (Bursell, 1958; Kleynhans & Terblanche, 2009) and desiccation resistance is a trait which is probably directly related to evolutionary fitness in this life stage (Bursell, 1958, 1959; Hargrove, 2004).…”

Effect of cuticular abrasion and recovery on water loss rates in queens of the desert harvester ant Messor pergandei

“…The positive association between WLR and environmental humidity can also vary through the life cycle, e.g. occurring in pupae but not in adults, indicating that selection exerts more pressure on some life stages than on others (Kleynhans and Terblanche, 2008). However, the association between water loss and environment is not universal because other factors, such as phylogenetic constraints, also exert a strong effect on water balance and WLRs (Grefen and Ar, 2004;Grefen and Ar, 2006).…”

Environmental Aspects of Zoonotic Diseases

“…Raising African cattle on large areas is hampered by the high pervasiveness of tsetse flies and altered agro-forestry practices (Ilemobade, 2009;Molyneux, 1998). Kleynhans and Terblanche (2009) showed that water loss rates (WLR) were significantly positively related to precipitation in pupa but not adults, suggesting that a reduction in WLR and increased size probably developed from a transitional ancestral state that may have facilitated survival in xeric environments. In this context, it should be mentioned that endemic human African trypanosomiasis (HAT) currently appears to be limited to areas where annual rainfall is higher than 1,200 mm, although the reasons for this remain unknown (Courtain et al, 2008).…”