Morphological variation and sex-biased frequency of wing dimorphism in the pygmy grasshopper Tetrix subulata (Orthoptera: Tetrigidae)

Anja STEENMAN,Arne W. LEHMANN,Gerlind U.C. LEHMANN

doi:10.14411/eje.2013.071

Abstract

Dimorphism in wing length is well known in many insect species. It is generally believed that a trade-off between dis- persal and reproduction exists, with the long-winged (LW) morph being a better disperser due to its superior flight capability. The short-winged (SW) morph is less mobile and it is hypothesised that females of this morph invest more of their energy reserves in producing offspring. We determined the variation in body and wing size in the pygmy grasshopper Tetrix subulata (Orthoptera: Tetrigidae). The results of the morphological study support the occurrence of two clearly distinct wing morphs in both sexes. SW individuals, especially males, were smaller and in accord with proposed developmental instability showed greater variability in body size than LW individuals. Using data for 700 wild-caught individuals from 10 populations, we demonstrate a variable frequency in the percentage of LW individuals, ranging from all-LW to all-SW populations, even if the LW morph is by far the most common morph in an area. The male-biased percentage of LW individuals recorded in intermediate populations supports a difference in the dispersal reproduction trade-off between the sexes.

Highlights

Where flight is the main dispersal mode, variation in dispersal ability and its morphological equivalent is widespread and found in numerous insect species (Harrison, 1980; Roff, 1986; Zera & Denno, 1997; Zera, 2009; Simpson et al, 2011) and has ecological and evolutionary consequences (Roff, 1994; Schwander & Leimar, 2011)
We determined the variation in body and wing size in the pygmy grasshopper Tetrix subulata (Orthoptera: Tetrigidae)
Using data for 700 wild-caught individuals from 10 populations, we demonstrate a variable frequency in the percentage of LW individuals, ranging from all-LW to all-SW populations, even if the LW morph is by far the most common morph in an area

Summary

Introduction

Where flight is the main dispersal mode, variation in dispersal ability and its morphological equivalent (wing polymorphism) is widespread and found in numerous insect species (Harrison, 1980; Roff, 1986; Zera & Denno, 1997; Zera, 2009; Simpson et al, 2011) and has ecological and evolutionary consequences (Roff, 1994; Schwander & Leimar, 2011). The majority of Orthoptera (grasshoppers, crickets and bushcrickets) in Central Europe are wingdimorphic or polymorphic (Harz, 1969, 1975; Ingrisch & Köhler, 1998). It is suggested that the high level of wing polymorphism is a result of repeated cycles of extensive glaciation in Central Europe during the last 2 million years (Hewitt, 2004; Schmitt, 2007). Recolonization from Asian and Mediterranean refuges may have favoured species with high colonization capacities, as proposed for wing-dimorphic carabid beetles (Aukema, 1995)

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