Latitudinal variation in thermal reaction norms of post-winter pupal development in two butterflies differing in phenological specialization

Abstract

Latitudinal clines in thermal reaction norms of development are a common phenomenon in temperate insects. Populations from higher latitudes often develop faster throughout the range of relevant temperatures (i.e countergradient variation) because they must be able to complete their life cycle within a shorter seasonal time window compared to populations at lower latitudes. In the present study, we experimentally demonstrate that two species of butterflies Anthocharis cardamines (L.) and Pieris napi (L.) instead show a cogradient variation in thermal reaction norms of post-winter pupal development so that lower latitude populations develop faster than higher latitude populations. The two species share host plants but differ in the degree of phenological specialization, as well as in the patterns of voltinism. We suggest that the pattern in A. cardamines, a univoltine phenological specialist feeding exclusively on flowers and seedpods, is the result of selection for matching to the phenological pattern of its local host plants. The other species, P. napi, is a phenological generalist feeding on the leaves of the hosts and it shows a latitudinal cline in voltinism. Because the latitudinal pattern in P. napi was an effect of slow development in a fraction of the pupae from the most northern population, we hypothesize that this population may include both bivoltine and univoltine genotypes. Consequently, although the two species both showed cogradient patterns in thermal reaction norms, it appears likely that this was for different reasons.

Winter chilling speeds spring development of temperate butterflies

“…In Sweden, the pattern corresponds to co‐gradient variation, as has been found experimentally (Posledovich et al . ; Stålhandske et al . ).…”

“…From previous experimental studies, we know that there is local adaptation in the A. cardamines phenology, both in how spring condition and winter duration affects flight time (Posledovich et al . , ; Stålhandske et al . ).…”

“…Spring phenology of the orange tip butterfly, Anthocharis cardamines , and the green‐veined white, Pieris napi , can depend both on spring conditions, where warmer springs speed up development (Posledovich et al . ; Stålhandske et al . ), and on winter conditions, where milder winters lead to delayed hatching (Posledovich et al .…”

The developmental race between maturing host plants and their butterfly herbivore – the influence of phenological matching and temperature

“…It is interesting to note that post‐winter pupal development of these A. cardamines populations shows a cogradient latitudinal pattern, with pupae from the southern population developing faster than pupae from the northern population throughout a relevant temperature range (Posledovich et al . , ; Stålhandske et al . ; Navarro‐Cano et al .…”

“…These butterfly populations are genetically differentiated with respect to post‐winter pupal development (Posledovich et al . ). We specifically ask whether these two aspects – phenological synchrony and thermal conditions – influence the suitability of different host plant species for butterfly development and survival, and to what degree host plant species differ in their capacity to outrace the developing larvae and successfully produce seeds.…”