- Closely related species have similar shapes but they can have very different color patterns. This means that color patterns evolve rapidly and that they can be used to tease species apart. This also suggests that the hermit crabs themselves use these color patterns to recognize the members of their own species. So, the apparition of new color patterns could lead to new species. To illustrate this rapid evolution in color patterns, compare these closely related species that live most of the time on branching corals: Calcinus minutus (from Guam), Calcinus rosaceus (from Oman) and Calcinus nitidus (from Moorea).
- Isolated islands and archipelagos such as Hawaii have several endemic species of Calcinus, which suggests that the formation of new species (speciation) happened on the edges of their geographical ranges.
- Most species of Calcinus are found in oceanic areas in particular in the Western Pacific and in Polynesia. This is different from what is known for other marine invertebrates. Indeed, in corals, fishes, and various groups of mollusks, most of the diversity is found in a more continental area called the "coral triangle" (from northern Australia to Indonesia and Papua New Guinea). To illustrate this difference, compare the 2 maps below. The first one shows the distribution of the diversity for the hermit crabs of the genus Calcinus whereas the map on the bottom is the same kind of map for the cowries. The unusual diversity pattern found in Calcinus highlights the importance of the ecological and historical processes characterizing each group of organism that have led to their current geographical distribution.
- Editor's choice. Science. 327 (26 March 2010): https://www.sciencemag.org/content/vol327/issue5973/twil.dtl#327/5973/1555-c
- Malay MC, Paulay G. 2010. Peripatric Speciation Drives Diversification and Distributional Pattern of Reef Hermit Crabs (Decapoda: Diogenidae: Calcinus). Evolution. 64-3:634-662. DOI: 10.1111/j.1558-5646.2009.00848.x
- Paulay G, Meyer C. Dispersal and divergence across the greatest ocean region : Do larvae matter ? Integrative and Comparative Biology. 2006;46(3):269-281. DOI: 10.1093/icb/icj027