Limited intrinsic postzygotic reproductive isolation despite chromosomal rearrangements between closely related sympatric species of small ermine moths (Lepidoptera: Yponomeutidae)

Abstract

In evolutionarily young species and sympatric host races of phytophagous insects, postzygotic incompatibility is often not yet fully developed, but reduced fitness of hybrids is thought to facilitate further divergence. However, empirical evidence supporting this hypothesis is limited. To assess the role of reduced hybrid fitness, we studied meiosis and fertility in hybrids of two closely related small ermine moths, Yponomeuta padella and Yponomeuta cagnagella, and determined the extent of intrinsic postzygotic reproductive isolation. We found extensive rearrangements between the karyotypes of the two species and irregularities in meiotic chromosome pairing in their hybrids. The fertility of reciprocal F1 and, surprisingly, also of backcrosses with both parental species was not significantly decreased compared with intraspecific offspring. The results indicate that intrinsic postzygotic reproductive isolation between these closely related species is limited. We conclude that the observed chromosomal rearrangements are probably not the result of an accumulation of postzygotic incompatibilities preventing hybridization. Alternative explanations, such as adaptation to new host plants, are discussed.

Speciation through chromosomal fusion and fission in Lepidoptera

“…Taken together, the evolution of chromosomal variation may be a significant factor for speciation, but its effect and magnitude seems to differ among (figure 4) and potentially within genera. The latter is indicated by the observation that the strength of reproductive isolation caused by differences in chromosome numbers can be limited when species have only recently diverged [10,11]. While some large-scale chromosomal rearrangements may act as DMIs, suggested by our inferred cases of cladogenetic chromosomal change (electronic supplementary material, S4.3), changes are more often anagenetic and may suggest that chromosomal rearrangements could, if at all, promote speciation by suppressing recombination in genomic regions underlying adaptation [6,7].…”

“…Nevertheless, empirical evidence for the role of varying chromosome numbers in speciation is mixed, in part contrasting the theoretical predictions. Closely related species with different chromosome numbers can often be crossed [8,9] and hybrid fitness may not necessarily be reduced [10,11]. Moreover, evolutionary modes of diversification within genera in relation to varying chromosome numbers may range from neutral [4,12] to adaptive [5] evolution.…”

A macroevolutionary role for chromosomal fusion and fission inErebiabutterflies

“…Our study bridges between these former investigations and microevolutionary studies that focus on one species or compare sibling species [e.g. 11,59,62 ] by demonstrating within-genus differences of chromosomal fusion-and fission-related speciation. We highlight that chromosomal speciation may be more relevant in clades with more diversity in preprint (which was not certified by peer review) is the author/funder.…”

“…The copyright holder for this this version posted January 18, 2023. ; https://doi.org/10.1101/2023.01. 16.524200 doi: bioRxiv preprint segregate correctly in hybrids [ 9,10,11 ]. Crosses between closely-related holocentric species with different karyotypes may remain viable [ 10 ] and do not necessarily result in reproductive isolation [ 11,12 ].…”

Incomplete Sterility of Chromosomal Hybrids: Implications for Karyotype Evolution and Homoploid Hybrid Speciation

“…Insects of the order Lepidoptera (i.e., butterflies and moths) have holocentric chromosomes (Murakami and Imai, 1974), and some species demonstrate inverted meiosis (Lukhtanov et al, 2018(Lukhtanov et al, , 2020, as well as a very high level of inter-and intrapopulation variation in karyotypes (Lukhtanov et al, 2011). Therefore, it is not surprising that the most extreme examples of viable chromosomal hybrids are found in this order (Nagaraju and Jolly, 1986;Traut and Clarke, 1997;Hora et al, 2019).…”