Biology subjects

Kralj-Fiser, S.

Publications and source records attributed to Kralj-Fiser, S..

5 recordsLinked to original sources

bioRxiv2026

High-quality reference genome of the African hermit spider, Nephilingis cruentata, and sex chromosome evolution in spiders

Background: Chromosome-level genome assemblies are increasingly enabling tests of chromosome evolution, conserved synteny, and sex chromosome conservation across diverse animal lineages, including spiders. Results: Here, we present a chromosome-level genome assembly for the African hermit spider, Nephilingis cruentata, a species with extreme female-biased sexual size dimorphism and a cytogenetically inferred XX2 sex chromosome system. The final Hi-C-assisted assembly spans 1.72 Gbp, with 99.5% of bases assigned to 13 pseudochromosomes, a scaffold N50 of 131.6 Mbp, and a BUSCO completeness score of 98.8%. We annotated 20,021 protein-coding genes, and repetitive elements accounted for 42.7% of the genome. Sex-specific whole-genome resequencing identified Chr02 and Chr07 as candidate X chromosomes based on reduced male coverage, consistent with the expected XX2 system. Using comparative whole-genome alignments across existing chromosome-scale spider assemblies, we also show that sex-linked chromosomes retain broad homologous identity across sampled spider lineages but exhibit lower synteny conservation and greater chromosome-length divergence than autosomes. Conclusions: These results suggest that spider sex chromosomes are conserved in homologous identity but more labile in structure, providing a comparative framework for studying sex chromosome conservation and divergence across Araneae.

genomics↗

bioRxiv2025

It is complicated: how sex, family, and season affect growth in a sexually size-dimorphic spider

Female-biased sexual size dimorphism (SSD), where females are larger than males, is widespread. While ultimate explanations for SSD are well established, the proximate developmental mechanisms remain poorly understood. Studying sex-specific growth trajectories to identify common vs. sex-specific growth periods is therefore key to uncovering when and how SSD emerges. Theory predicts that female-biased SSD may arise if females hatch larger, grow more rapidly, grow longer, or combine these pathways. We studied sex-specific growth trajectories in the African hermit spider, Nephilingis cruentata, where adult females are on average 75-times heavier and take 2.3-times longer until adulthood than males. We tracked growth trajectories of carapace width for 916 individuals. After initial growth trajectories common to both sexes, trajectories diverged after [~]80 days, coinciding with the onset of the male subadult stage. At this point, male growth decelerated and terminated at sexual maturity, whereas female growth accelerated until their subadult stage at [~]200 days. Thereafter, female growth rate also decelerated and eventually terminated at sexual maturity. Thus, females attain their larger size through both an extended growth period and a more rapid growth rate, which initiates in mid-development. Whereas we detected seasonal effects on growth that were similar in both sexes, family effects showed strong sex-specific signatures. Our results pinpoint a key developmental window in which male and female growth trajectories begin to diverge, providing a clear target for detailed investigation of the mechanisms underlying SSD. At the same time, the complexity of these patterns will likely hinder mechanistic studies of SSD development.

zoology↗

bioRxiv2022

Sexual conflict mitigation via sex-specific trait architecture

Sexual dimorphism -- the sex-specific trait expression -- may emerge when selection favours different optima for the same trait between sexes, i.e., under antagonistic selection. Intra-locus sexual conflict exists when the sexually dimorphic trait under antagonistic selection is based on genes shared between sexes. A common assumption for sexual-size dimorphism (SSD) is that its presence indicates resolved sexual conflict, but how current sex-specific evolution proceeds under sexual dimorphism remains enigmatic. We investigated whether a sex-specific architecture of adult body size explains sexual conflict resolution under extreme SSD in the African hermit spider, Nephilingis cruentata, where adult female body size greatly exceeds that of males. Specifically, we estimated the sex-specific importance of genetic and maternal effects on adult body size among individuals that we laboratory-reared for up to eight generations. Quantitative genetic model estimates indicated that size variation in females is to a larger extent explained by direct genetic effects than by maternal effects, but in males to a larger extent by maternal than by genetic effects. We conclude that this sex-specific body-size architecture enables body-size evolution to proceed much more independently than under a common architecture to both sexes, thereby mitigating sexual conflict under SSD.

evolutionary biology↗

bioRxiv2022

Quantitative genetic study suggests sex-specific genetic architecture for fetal testosterone in a wild mammal

Testosterone plays a critical role in mediating fitness-related traits in many species. Although it is highly responsive to environmental and social conditions, evidence from several species show a heritable component to its individual variation. Despite the known effects that in utero testosterone exposure have on adult fitness, the heritable component of individual testosterone variation in fetuses is mostly unexplored. Furthermore, testosterone has sex-differential effects on fetal development, i.e., a specific level may be beneficial for male fetuses but detrimental for females. The above mentioned may lead to a different genetic structure underlying the heritability of testosterone between the sexes. Here, we used a wild animal model, the feral nutria, quantified testosterone using hair-testing and estimated its heritability between parent and offspring from the same and opposite sex. We found that in utero accumulated hair testosterone levels were heritable between parents and offspring of the same sex. However, there was a low additive genetic covariance between the sexes, and a relatively low cross-sex genetic correlation, suggesting a potential for sex-dependent trait evolution, expressed early on, in utero.

molecular biology↗

bioRxiv2020

Sex-Specific Genetic Architecture Of Behavioral Traits In A Spider

Sex differences in behavioral traits are common, but we know little about the role of sexual selection in shaping these traits. Estimating sex-specific genetic effects and cross-sex genetic correlations can provide insights into sex-specific selection and on whether evolution can shape independent expression of behavioral traits across the sexes. We conducted a quantitative genetic study in a sexually-size-dimorphic spider, Larinioides sclopetarius, which exhibits sex differences in adult life-styles. We observed pedigreed spiders for aggression, activity, exploration and boldness, and used animal models to disentangle genetic and environmental influences on these behaviors. We detected higher additive genetic variances in activity and aggression in males compared to females, but no sex differences in quantitative genetic estimates for exploration and boldness. The estimated mean cross-sex genetic correlation in all traits were close to zero suggesting these traits could have flexibility for sex-independent evolution. We note however, that the 95% credible intervals of cross-sex genetic correlation are large, and thus estimates uncertain. Our results imply that individual variation in aggression and activity might stem from sex-specific selection acting on these traits. The estimates of sex-specific additive genetic variation and cross-sex genetic correlation suggests their further sex-independent evolution. Taken together, our results support the notion that sexual selection can play an important role shaping behavioral traits.

evolutionary biology↗