Wing morphological responses to latitude and colonisation in a range expanding butterfly

Abstract

Populations undergoing rapid climate-driven range expansion experience distinct selection regimes dominated both by increased dispersal at the leading edges and steep environmental gradients. Characterisation of traits associated with such expansions provides insight into the selection pressures and evolutionary constraints that shape demographic and evolutionary responses. Here we investigate patterns in three components of wing morphology (size, shape, colour) often linked to dispersal ability and thermoregulation, along latitudinal gradients of range expansion in the Speckled Wood butterfly (Pararge aegeria) in Britain (two regions of expansion in England and Scotland). We measured 774 males from 54 sites spanning 799 km with a 10-year mean average temperature gradient of 4 °C. A geometric morphometric method was used to investigate variation in size and shape of forewings and hindwings; colour, pattern, and contrast of the wings were examined using a measure of lightness (inverse degree of melanism). Overall, wing size increased with latitude by ∼2% per 100 km, consistent with Bergmann’s rule. Forewings became more rounded and hindwings more elongated with history of colonisation, possibly reflecting selection for increased dispersal ability. Contrary to thermal melanism expectations, wing colour was lighter where larvae developed at cooler temperatures and unrelated to long-term temperature. Changes in wing spot pattern were also detected. High heterogeneity in variance among sites for all of the traits studied may reflect evolutionary time-lags and genetic drift due to colonisation of new habitats. Our study suggests that temperature-sensitive plastic responses for size and colour interact with selection for dispersal traits (wing size and shape). Whilst the plastic and evolutionary responses may in some cases act antagonistically, the rapid expansion of P. aegeria implies an overall reinforcing effect between these two mechanisms.

Wing morphology and eyespot pattern of Erebia medusa (Lepidoptera, Nymphalidae) vary along an elevation gradient in the Carpathian Mountains

“…Restrictions of the movement and migration of butterfly species have an impact on the intensity and direction of gene flow between populations (Andrews 2010;Slatkin and Excoffier 2012). Characterisation of the morphological traits of E. medusa, a species inhabiting a wide range of environments, can provide insight into the selection pressures that affect adaptive responses (Cespedes et al 2015;Taylor-Cox et al 2020).…”

Reduced host‐plant specialization is associated with the rapid range expansion of a Mediterranean butterfly

“…While ecological processes have often been found to underlie range shifts, evidence for a crucial role of evolutionary processes is still relatively scarce (Benito Garzón et al, 2019; Hill et al, 2011). Most examples for rapid evolution associated with range shifts relate to dispersal‐related morphology (Simmons & Thomas, 2004; Taylor‐Cox et al, 2020), but also physiology (Leonard & Lancaster, 2020; Liebl & Martin, 2013), life history (Phillips et al, 2010) and behaviour including resource use (Lancaster, 2020; Singer & Parmesan, 2020; Thomas et al, 2001).…”

Ontogenetic shape trajectory of Trichomycterus areolatus varies in response to water velocity environment

“…Environmental variation can also lead to intraspecific morphometric differentiation [ 13 – 17 ]. Examples include differences in head shape in wall lizards ( Podarcis bocagei ) between saxicolous and ground-dwelling habitats; wing morphology in speckled wood butterflies ( Parage aegeria ) along a latitudinal gradient; tail, head and ear length in West African Dwarf goats ( Capra aegagrus hircus ) among agro-ecological zones and swimming performance and shape in Creek Chub ( Semotilus atromaculatus ) due to urbanization [ 18 – 21 ]. Such intraspecific phenotypic variation can be the result of genetic [ 22 ] or plastic variation [ 23 – 25 ].…”