The role of macropters during range expansion of a wing-dimorphic insect species

Abstract

Marked changes in distribution in consequence of global warming have been observed not only for highly mobile insect taxa, which are capable of flight, but also for wing-dimorphic species with predominantly short-winged individuals. In the special case of wing-dimorphic species, it is likely that the rarer long-winged (macropterous) morph plays an important role in the dispersal process, but little is known about how and to what extent it is involved. The aim of our study was to provide more information on the mechanisms behind dispersal processes in wing-dimorphic insects at expanding range margins. As solitary individuals are believed to play an important role in the range expansion of wing-dimorphic species (potential dispersers), we recorded the number of long-winged and short-winged solitary males at the local range margin of our model organism Metrioptera roeselii (Orthoptera: Tettigoniidae) in NW Germany. To investigate differences in dispersal capability (% macropters) between populations with different colonisation histories, we studied 43 populations of M. roeselii. Our results show that about 2/3 of the solitary males were long-winged and these long-winged individuals were significantly more frequent in recently colonised areas. Moreover, M. roeselii had a significantly higher dispersal capability (% macropters) in high-density populations and in recently established populations at the expanding range margin compared to populations characterised by medium-or long-term establishment nearer to the range core. Our study is the first that quantifies the importance of macropters for the recent range expansion of a wing-dimorphic species and it provides for the first time detailed insights into the complex dispersal processes that take place at the expanding range margin. It is likely that density stress and a changed genetic predisposition to become macropterous, and thus a combination of both ecological and evolutionary effects, leads to a high percentage of macropters in recently colonised areas.

Two Species with an Unusual Combination of Traits Dominate Responses of British Grasshoppers and Crickets to Environmental Change

“…roeselii and C . discolor : multiple studies suggest both species are expanding their ranges successfully through a combination of effective dispersal (aided by high numbers of macropterous individuals) and subsequent high reproductive rates (of brachypters); selection for increased dispersal at the advancing range margin appears to be reinforcing the process [ 18 , 19 , 40 , 80 , 91 , 92 ]. Wing-length is not identified as a significant predictor of range change in our analysis.…”

Expanding population edges: theories, traits, and trade‐offs

“…While brachypters are limited in dispersal ability, macropters are able to Cwynar & MacDonald (1987) engage in strong pulses of long-distance range expansion under favorable environmental conditions (Hochkirch & Damerau, 2009). Multiple studies have reported higher proportions of macropterous individuals at recently colonized range fronts, suggesting that these dispersal-oriented morphs may act as the initial Morphology Achene size Bartle et al (2013) colonists prior to population establishment [crickets (Thomas et al, 2001;Simmons & Thomas, 2004;Poniatowski et al, 2012) and beetles (Niemela & Spence, 1991, 1999]. Not only can the frequency of dispersal morphs differ across an expanding range, but the dispersal ability of macropterous individuals may be elevated at the margins.…”

A Review of the Phenotypic Traits Associated with Insect Dispersal Polymorphism, and Experimental Designs for Sorting out Resident and Disperser Phenotypes

“…This experimental study was conducted to simulate the evolution of dispersal traits at invasion fronts, and revealed that variability of the measured traits was also increased in these individuals. In wing-dimorphic insects, range shifting is also associated with an increase of the dispersal capacities of the macropterous individuals from expansion range margins [181]. Moreover, the higher occurrence of macropters of the cricket Metrioptera roeselii in recently colonized areas reveals the crucial role played of this insect morph during range expansion [181].…”