Abstract
The ladybird beetle Cheilomenes sexmaculata (Fabricius) is widely distributed throughout the intermediate latitudinal and equatorial regions. It exhibits elytral colour polymorphism with a geographical cline showing increased prevalence of melanic morphs with increasing latitude. Over the past 100 years, this species has extended its distribution towards higher latitudes in Japan because of climatic warming. In this study, long-term changes in the frequency of different morphs and adult body size of this species during this range extension were analyzed based on a survey of specimens in collections. First, we examined specimens collected from areas that were colonized (34-36°N) during the period of range extension (1949-1989) and when it ceased (1990-2005). Chronologically, both the proportions of melanic morphs increased and body size decreased significantly. Next, specimens were examined from newly colonized regions and the former range of distribution (32-34°N); these specimens were collected during period when range extension had ceased. In newly colonized regions, the frequency of melanic morphs was higher and the body size was smaller than in the former range of distribution. These two findings indicate that the smaller, melanic morphs may have undergone a positive-selection driven range extension to higher latitudes.
Highlights
Insects that are distributed widely are known to exhibit various changes in their life history traits in response to spatial and temporal variations in habitat (Masaki, 1974)
Morph frequency and adult body size of C. sexmaculata collected during different periods of the range extension
There was a significant difference in the morph frequency of specimens collected during the period when range extension had ceased (1990–2005) in the newly colonized areas (34–36°N) and those in the area of the original ladybird distribution prior to the 1940s (32–34°N) (Fig. 3; male: df = 3, χ2 = 25.3653, P < 0.0001, female: df = 3, χ2 = 12.2335, P = 0.0066)
Summary
Insects that are distributed widely are known to exhibit various changes in their life history traits in response to spatial and temporal variations in habitat (Masaki, 1974). In the process of range extension, changes in insect phenotypes are recorded that are associated with adapting to the newly colonized areas In the cases of (2) and (3), changes in traits that are associated with adapting to changes in climate may occur during the process of northward extension. Studies of the relationship between trait change and northward extension, may provide insight into the invasion and subsequent spread of non-native insects in response to climate change
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
