DOI: 10.5061/dryad.5x69p8dc0
title: From darkness to twilight: Morphological divergence between cave and surface-subterranean ecotone Niphargus species

description: Subterranean and surface habitats are in stark contrast in several
 environmental factors. Therefore, adaptation to the subterranean
 environment typically impedes the (re)colonisation of surface habitats.
 The genus Niphargus includes amphipod crustaceans that primarily occupy
 subterranean habitats. All its species show typical adaptations to the
 subterranean environment. However, some Niphargus species occur in
 surface-subterranean ecotones. To understand whether (i) habitat
 divergence is present between the cave and the ecotone species (ii)
 similar phenotypes emerge independently in every ecotone, we studied
 morphological divergence between four cave and four ecotone Niphargus
 species based on 13 functional morphological traits. To account for
 different selection acting on the sexes, we included males (N = 244) and
 females (N = 222). Nine out of 13 traits showed habitat- divergence.
 Traits related to feeding and crawling were shorter in ecotone species,
 while traits related to oxygenation were larger in ecotone species. Eleven
 out of 13 traits were sexually dimorphic. Traits related to oxygenation
 and crawling were larger in females, while the trait related to swimming
 was larger in males. We found that the extent of sexual dimorphism differs
 between the habitats in eight traits related to sensing, feeding,
 oxygenation and crawling. Additionally, we found that in certain traits
 related to sensing and oxygenation, habitat related differences are only
 present in case of one but not the other sex. We conclude that the
 detected differences between the cave and the ecotone species indicate
 divergent evolution, where similarities among the different species within
 a habitat type indicate convergent evolution. The high degree of sexual
 dimorphism paired with differences in sexual dimorphism between the
 habitats in certain traits suggest that sexual and fecundity selections
 have comparable effects to environmental selection. Thus, studies of
 habitat-dependent adaptations investigating one sex only, or not
 considering sexual dimorphism, can lead to erroneous conclusions. --
description: # From darkness to twilight: Morphological divergence between cave and
 surface-subterranean ecotone Niphargus species
 [https://doi.org/10.5061/dryad.5x69p8dc0](https://doi.org/10.5061/dryad.5x69p8dc0) The data contains morphological measurements of 13 traits plus the body length of eight species of the *Niphargus *genus. The traits were measured on microscope slides except for body length which was measured using photos. The dataset contains the R script used for analysis. ## Description of the data and file structure The original data file contains linear measurements of the given traits in millimeter. Species_abbreviation in the original data denote the following species:  POD - Niphargus podpecanus; SPO - Niphargus spoeckeri; SCO - Niphargus scopicauda; STY - Niphargus stygius; TIM - Niphargus timavi; SPH - Niphargus sphagnicolus; SPI - Niphargus spinulifemur; KRA - Niphargus krameri ## Sharing/Access information ## Code/Software The R code used for the analysis is called Biroetal_Fromdarkness_code and is uploaded to Zenodo in the linked repository.