Abstract
Traits of thermal sensitivity or performance are typically the focus of species distribution modelling. Among-population trait variation, trait plasticity, population connectedness and the possible climatic covariation thereof are seldom accounted for. Here, we examine multiple climate stress resistance traits, and the plasticity thereof, for a globally invasive agricultural pest insect, the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). We also accounted for body size and population genetic connectivity among distinct populations from diverse bioclimatic regions across southern Africa. Desiccation resistance, starvation resistance, and critical thermal minimum (CTmin) and maximum (CTmax) of C. capitata varied between populations. For thermal tolerance traits, patterns of flexibility in response to thermal acclimation were suggestive of beneficial acclimation, but this was not the case for desiccation or starvation resistance. Population differences in measured traits were larger than those associated with acclimation, even though gene flow was high. Desiccation resistance was weakly but positively affected by growing degree-days. There was also a weak positive relationship between CTmin and temperature seasonality, but CTmax was weakly but negatively affected by the same bioclimatic variable. Our results suggest that the invasive potential of C. capitata may be supported by adaptation of tolerance traits to local bioclimatic conditions.
Highlights
While it is widely accepted that the geographic distributions of animal and plant species can be tightly correlated with environmental factors, the evolutionary and ecological determinants of such correlations are less clear
Ceratitis capitata populations were sampled at eight sites in regions of southern Africa with different climates spanning a latitudinal range of c. 32° (Table 1)
In D. melanogaster, for example, differences have been detected in desiccation resistance, starvation resistance, and size between geographic regions, there was higher variability between strains collected at multiple sites in each region[50]
Summary
While it is widely accepted that the geographic distributions of animal and plant species can be tightly correlated with environmental factors, the evolutionary and ecological determinants of such correlations are less clear. Apart from genetic factors such as inbreeding depression or low additive genetic variance that may explain trait variation and adaptive evolutionary potential in small populations[2,3], an emerging body of research proposes that ecological traits dictate species-environment relationships through fundamental evolutionary limits at the species level[4,5,6]. The generality of such an explanation requires further scrutiny because it presupposes limited intraspecific variation. The ecological impact of C. capitata in its invasive range has been far more modest; in combination with two other invasive fruit fly species, Bactrocera zonata (Saunders) and C. rosa Karsch, C. capitata competitively excludes an indigenous fruit fly, C. catoirii Guérin-Mèneville, on the island of Réunion[30]
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