A new species of freshwater crab genusFrediusPretzmann, 1967 (Crustacea: Brachyura: Pseudothelphusidae) from a naturally isolated orographic forest enclave within the semiarid Caatinga in Ceará, northeastern Brazil

Livanio C Santos,Allysson P Pinheiro,José R.F Silva,Marcelo Cervini,William Santana,Marcos Tavares

doi:10.7717/peerj.9370

Abstract

A new species of freshwater crab, Fredius ibiapaba, is described and illustrated from a mid-altitude forested patch in Ipú (Ibiapaba plateau, Ceará, northeastern Brazil), between 635 to 782 m. The new species can be separated from its congeners by the morphology of its first gonopod: proximal half remarkably swollen, sloping abruptly downwards distally to a nearly right-angular shoulder; mesial lobe much smaller than cephalic spine; cephalic lobe moderately developed; auxiliary lobe lip, delimiting field of apical spines, protruded all the way to distal margin of auxiliary lobe. Comparative 16S rDNA sequencing used to infer the phylogenetic placement of Fredius ibiapaba n. sp. revealed that it is the sister taxon of F. reflexifrons, a species which occurs allopatrically in the Amazon and Atlantic basin’s lowlands (<100 m). Fredius ibiapaba n. sp. and F. reflexifrons are highly dependent upon humidity and most probably were once part of an ancestral population living in a wide humid territory. Shrinking humid forests during several dry periods of the Tertiary and Quaternary likely have resulted in the fragmentation of the ancestral humid area and hence of the ancestral crab population. Fredius reflexifrons evolved and spread in a lowland, humid river basin (Amazon and Atlantic basins), whilst F. ibiapaba n. sp. evolved isolated on the top of a humid plateau. The two species are now separated by a vast intervening area occupied by the semiarid Caatinga

Highlights

Cumulative evidence from many independent sources argue in favor of the mid-altitude forested patches in northeastern Brazil being remnants of a once much larger humid forest, connected to both the Amazonian and Atlantic rainforests during the moister periods (e.g., Andrade-Lima, 1982; Cartelle & Hartwig, 1996; De Vivo, 1997; Ab’Saber, 2000; Auler et al, 2004; Carnaval & Bates, 2007; Carmignotto, De Vivo & Langguth, 2012; and references therein)
Evidence from a phylogenetic analysis using 16S rDNA is presented for a sister taxa relationship between Fredius ibiapaba n. sp. and F. reflexifrons (Ortmann, 1897), a species occurring allopatrically in the Amazonian humid lowlands
The sister species relationships between Fredius reflexifrons and the new species is well supported by high bootstrap value

Summary

Introduction

Cumulative evidence from many independent sources argue in favor of the mid-altitude forested patches in northeastern Brazil being remnants of a once much larger humid forest, connected to both the Amazonian and Atlantic rainforests during the moister periods (e.g., Andrade-Lima, 1982; Cartelle & Hartwig, 1996; De Vivo, 1997; Ab’Saber, 2000; Auler et al, 2004; Carnaval & Bates, 2007; Carmignotto, De Vivo & Langguth, 2012; and references therein). Previous hypothesis on the phylogenetic relationships of F. reflexifrons and the possible evolutionary scenario that led to the emergence of the sister taxa Fredius ibiapaba n. sp. and F. reflexifrons are discussed

Methods

Results

Conclusion