Biogeography and morphological evolution in a Pacific island ant radiation

Area of Science:

• Evolutionary Biology
• Ecology
• Entomology

Background:

• Insular radiations are common in terrestrial arthropods, but rare in eusocial insects.
• The spinescence in Fijian Pheidole ants raises questions about its origin: inherited trait or ecological adaptation?
• Previous hypotheses suggest the Fijian Pheidole roosevelti group is monophyletic, spinescence is ancestral, and they are related to New Guinean relatives.

Purpose of the Study:

• To investigate the evolutionary origins of spinescence in Fijian Pheidole ants.
• To test hypotheses regarding the monophyly of the P. roosevelti group, the ancestral nature of spinescence, and phylogenetic relationships with New Guinean ants.
• To understand morphological convergence, insular radiation, and Pacific biogeography in eusocial insects.

Main Methods:

• Phylogenetic analysis using mitochondrial (COI, cytb) and nuclear (H3, EF1α-F2) gene fragments.
• Inclusion of 66 taxa: all P. roosevelti group members, spinescent subgenus Pheidolacanthinus, Fijian congeners, and Pacific congeners.
• Comparative analysis to assess biogeographic history and evolutionary relationships.

Main Results:

• The study provides new insights into Fiji's biogeographic history.
• A compelling example of convergent evolution and ecological release in an insular eusocial insect lineage was identified.
• Fijian Pheidole ants colonized Fiji in the Miocene and radiated into niches occupied by distantly related, spinescent congeners elsewhere in the Pacific.

Conclusions:

• The radiation of Fijian Pheidole into spinescent morphotypes was driven by ecological opportunities.
• The absence of competing ant lineages with conspicuous epigaeic foraging strategies facilitated this radiation.
• This study serves as a novel example of ecological release shaping evolution in insular eusocial insects.