Biology subjects

Pitnick, S.

Publications and source records attributed to Pitnick, S..

3 recordsLinked to original sources

bioRxiv2026

Sperm length ornamentation associates with survival and sterility after heatwaves among Drosophila species

Whether sexual selection facilitates or hinders adaptation to novel environments is a question of fundamental importance due to current rapid environmental change. Using phylogenetic comparative analysis in 42 Drosophila species, we found that sperm length - a sexually selected ornament - positively associates with the ability of males to survive high temperatures. However, the ability to remain fertile does not increase with sperm length to the same extent, meaning that longer sperm species experience a larger gap between temperatures that kill and temperatures that sterilize males. The findings are consistent with the idea that strong sexual selection on condition-dependent exaggerated traits may facilitate somatic resilience to environmental stressors, but that susceptibility to heat-induced infertility may be a cost of extreme sperm ornamentation. Overall, the data suggests multifaceted links between postcopulatory sexual selection and climate change.

evolutionary biology↗

bioRxiv2023

Single-fly assemblies fill major phylogenomic gaps across the Drosophilidae Tree of Life

Long-read sequencing is driving rapid progress in genome assembly across all major groups of life, including species of the family Drosophilidae, a longtime model system for genetics, genomics, and evolution. We previously developed a cost-effective hybrid Oxford Nanopore (ONT) long-read and Illumina short-read sequencing approach and used it to assemble 101 drosophilid genomes from laboratory cultures, greatly increasing the number of genome assemblies for this taxonomic group. The next major challenge is to address the laboratory culture bias in taxon sampling by sequencing genomes of species that cannot easily be reared in the lab. Here, we build upon our previous methods to perform amplification-free ONT sequencing of single wild flies obtained either directly from the field or from ethanol-preserved specimens in museum collections, greatly improving the representation of lesser studied drosophilid taxa in whole-genome data. Using Illumina Novaseq X Plus and ONT P2 sequencers with R10.4.1 chemistry, we set a new benchmark for inexpensive hybrid genome assembly at US $150 per genome while assembling genomes from as little as 35 ng of genomic DNA from a single fly. We present 183 new genome assemblies for 179 species as a resource for drosophilid systematics, phylogenetics, and comparative genomics. Of these genomes, 62 are from pooled lab strains and 121 from single adult flies. Despite the sample limitations of working with small insects, most single-fly diploid assemblies are comparable in contiguity (>1Mb contig N50), completeness (>98% complete dipteran BUSCOs), and accuracy (>QV40 genome-wide with ONT R10.4.1) to assemblies from inbred lines. We present a well-resolved multi-locus phylogeny for 360 drosophilid and 4 outgroup species encompassing all publicly available (as of August 2023) genomes for this group. Finally, we present a Progressive Cactus whole-genome, reference-free alignment built from a subset of 298 suitably high-quality drosophilid genomes. The new assemblies and alignment, along with updated laboratory protocols and computational pipelines, are released as an open resource and as a tool for studying evolution at the scale of an entire insect family.

evolutionary biology↗

bioRxiv2019

Female x male and male x male interactions have limited influence on competitive fertilization in Drosophila melanogaster

How males and females contribute to joint reproductive success has been a long-standing question in sexual selection. Under postcopulatory sexual selection (PSS), paternity success is predicted to derive from complex interactions among females engaging in cryptic female choice and males engaging in sperm competition. Such interactions have been identified as potential sources of genetic variation in sexually selected traits but are also expected to inhibit trait diversification. To date, studies of interactions between females and competing males have focused almost exclusively on genotypes and not phenotypic variation in sexually selected traits. Here, we characterize within- and between-sex interactions in Drosophila melanogaster using isogenic lines with heritable variation in both male and female traits known to influence competitive fertilization. We found surprisingly few genotypic interaction effects on various stages of PSS such as female remating interval, copulation duration, sperm transfer, or sperm storage. Only the timing of female sperm ejection depended on female x male genotypic interactions. By contrast, several reproductive events, including sperm transfer, female sperm ejection and sperm storage, were explained by two- and three-way interactions among sex-specific phenotypes. We also documented complex interactions between the lengths of competing males sperm and the female seminal receptacle, which are known to have experienced rapid female-male co-diversification. Our results highlight the non-independence of sperm competition and cryptic female choice and demonstrate that complex interactions between the sexes do not limit the ability of multivariate systems to respond to directional sexual selection.\n\nSignificance statementFor species with internal fertilization and female promiscuity, postcopulatory sexual selection (PSS) is believed to depend, in part, on complex interactions between rival males and between the sexes. Although little investigated, clarifying such interactions is critical as they may limit the efficacy of PSS in the diversification of reproductive traits (e.g., ejaculate biochemistry and sperm, genitalia and female reproductive tract morphology). Here, we resolve how sex-specific traits and their interactions contribute to key reproductive events and outcomes related to competitive fertilization success, including traits known to have experienced rapid diversification. Our results provide novel insights into the operation and complexity of PSS and demonstrate that the processes of sperm competition and cryptic female choice are not independent selective forces.

evolutionary biology↗