Recombination in the eggs and sperm in a simultaneously hermaphroditic vertebrate

Abstract

When there is no recombination (achiasmy) in one sex, it is in the heterogametic one. This observation is so consistent that it constitutes one of the few patterns in biology that may be regarded as a 'rule ' and Haldane (Haldane 1922 J. Genet. 12, 101-109. (doi:10.1007/BF02983075)) proposed that it might be driven by selection against recombination in the sex chromosomes. Yet differences in recombination rates between the sexes (heterochiasmy) have also been reported in hermaphroditic species that lack sex chromosomes. In plants-the vast majority of which are hermaphroditic-selection at the haploid stage has been proposed to drive heterochiasmy. Yet few data are available for hermaphroditic animals, and barely any for hermaphroditic vertebrates. Here, we leverage reciprocal crosses between two black hamlets (Hypoplectrus nigricans, Serranidae), simultaneously hermaphroditic reef fishes from the wider Caribbean, to generate high-density egg-and spermspecific linkage maps for each parent. We find globally higher recombination rates in the eggs, with dramatically pronounced heterochiasmy at the chromosome peripheries. We suggest that this pattern may be due to female meiotic drive, and that this process may be an important source of heterochiasmy in animals. We also identify a large non-recombining region that may play a role in speciation and local adaptation in Hypoplectrus.

Inter-chromosomal coupling between vision and pigmentation genes during genomic divergence

“…To test these hypotheses, we assembled a reference genome for the hamlets. We used a combination of Illumina (245×) and PacBio (10×) data to assemble scaffolds, which were then anchored to a high-density linkage map including 24 linkage groups (denoted by 'LG' followed by a number) 26 , matching the 24 chromosomes expected in serranids 27 . The resulting assembly was 612 megabases (Mb) long with 92% of scaffolds anchored to the linkage map, resulting in a super-scaffold n50 of 24 Mb.…”

“…The resulting scaffolds were additionally gap closed with the Illumina-corrected PacBio data using PBjelly 71 (git 1.2.4.1−1.2.4.6). Finally, the twofold gap-closed scaffolds were anchored and oriented to two RAD-based hamlet linkage maps 26 using Allmaps 72 . Briefly, the linkage map RAD tags were mapped onto the assembly scaffolds using Bowtie2 and the physical positions of the markers on the scaffolds were retrieved.…”

Low recombination rates in sexual species and sex–asex transitions

“…(a) Low chromosome numbers [60]. The C. elegans example is particularly interesting as it shows low recombination rates in chromosomal centres, but these are not associated with the presence of centromeres.…”

Temporal changes in hamlet communities (Hypoplectrus spp., Serranidae) over 17 years

“…The hamlets, simultaneously hermaphroditic sea basses from the tropical western Atlantic Ocean (Hypoplectrus spp., Perciformes: Serranidae), have intrigued ichthyologists for decades (Barlow, 1975;Fischer & Petersen, 1987;Domeier, 1994;McCartney et al, 2003;Theodosiou et al, 2016). Seventeen species are now recognized, a third of which have been described in the past few years (Del Moral Flores et al, 2011;Lobel, 2011;Victor, 2012;Tavera & Acero, 2013).…”

“…The hamlets have served as a distinctive model system for the study of a variety of ecological and evolutionary processes including the evolution and maintenance of simultaneous hermaphroditism (Fischer, 1980b), sex allocation (Fischer, 1981), egg trading (Fischer & Petersen, 1987), sexual selection (Puebla et al, 2011), dispersal (Puebla et al, 2009), local adaptation (Picq et al, 2016), speciation (Holt et al, 2011), evolutionary radiation (Puebla et al, 2008) and recombination (Theodosiou et al, 2016). Temporal changes in hamlet communities can potentially affect or be affected by such processes.…”