Past and current climate as a driver in shaping the distribution of the Longitarsus candidulus species group (Coleoptera: Chrysomelidae)

Abstract

Longitarsus candidulus (Foudras) is a thermophilic flea beetle species widely distributed in the Mediterranean Basin and associated with Daphne gnidium L. and Thymelaea hirsuta (L.). Longitarsus laureolae Biondi and Longitarsus leonardii Doguet, phylogenetically closely related to L. candidulus, show together a peculiar and rare disjunct distribution along the central-southern Apennines and the Cantabrian-Pyrenean mountain system, respectively. Both are associated with Daphne laureola L. in mesophilic habitats. We used "ecological niche modeling" to infer the Pleistocene dynamics in the distribution of the three flea beetle species and their host plants. We interpreted their current distributions, paying particular attention to the presumed time of species divergence as inferred from recent studies. The differentiation of L. laureolae and L. leonardii from L. candidulus likely represents a response to the marked climatic changes during the Late Pliocene. Such a split was likely associated with a trophic niche shift of the laureolae/leonardii ancestor towards the typically mesophilic host plant D. laureola. The subsequent split between L. laureolae and L. leonardii, possibly due at first to the niche competition, was then boosted by an allopatric divergence during the Middle Pleistocene, likely caused by a large area of low environmental suitability for both species, mainly located between the northern Apennines and the south-western Alps.

Keywords: Alticini; Thymelaeaceae; ecological modeling; marine isotope stage 19.

Fig. 1.

Habitus, aedeagus, and spermatheca of the Longitarsus candidulus species group, modified from Berrilli et al. (2024). A) Longitarsus candidulus (Foudras). B) Longitarsus laureolae Biondi. C) Longitarsus leonardii Doguet. For each species, the habitus (left), the median lobe of the aedeagus (top right) in ventral, dorsal, and lateral view (from left to right), and the spermatheca (bottom right) are shown. Original figure used by permission of Current Zoology.

Fig. 2.

Occurrence localities. A) Longitarsus candidulus species group. B) Host plants of the Longitarsus candidulus species group.

Fig. 3.

Distribution models in the CURRENT climatic conditions. A) Longitarsus candidulus. B) Daphne gnidium and Thymelaea hirsuta. C) Longitarsus laureolae. D) Daphne laureola. E) Longitarsus leonardii. F) Histogram of the insect-insect and insect-host plant correlations. (A)–(E): different colors refer to different probabilities of presence, as in the legends.

Fig. 4.

Distribution models in the MIS19 climatic conditions. A) Longitarsus candidulus. B) Daphne gnidium and Thymelaea hirsuta. C) Longitarsus laureolae. D) Daphne laureola. E) Longitarsus leonardii. F) Histogram of the insect–insect and insect–host plant correlations. (A)–(E): different colors refer to different probabilities of presence, as in the legends. (C, E): the black line pointed by the arrow delimits the area at low suitability hypothesized for L. laureolae and L. leonardii.

Fig. 5.

Values of the variable BIO8 (mean temperature of wettest quarter) of the Longitarsus candidulus species group and their host plants in the CURRENT model. A) Comparison between flea beetle species. B–D) Comparison between each flea beetle species and host plants.

Fig. 6.

Values of the variables that most contributed to the separation between the suitability areas of Longitarsus candidulus, L. laureolae, and L. leonardii in the MIS19 model. A) BIO8 (mean temperature of wettest quarter). B) BIO9 (mean temperature of driest quarter). C) BIO14 (precipitation of driest period). D) BIO19 (precipitation of coldest quarter).

Fig. 7.

Cumulative areas in the CURRENT and MIS19 models, at 51–75% and 76–100% of suitability, for the Longitarsus candidulus species group and their host plants.