Luis Rodrigo Arce-Valdés

Sexual and natural selection jointly contribute to the rapid evolution of mating-related traits, making hybridizing systems particularly informative for exploring how different classes of traits diverge during early speciation. The damselflies Ischnura elegans and Ischnura graellsii form two hybrid zones in Spain that differ in demographic structure and spatial genetic patterns, providing a natural framework to compare patterns of divergence in reproductive (male caudal appendages and the female prothorax) and non-reproductive (wings) traits. Using geometric morphometrics within a phylogenetic comparative framework, together with population genetic information, we compared evolutionary integration, rates of divergence, and evolutionary dynamics across traits and species. In I. elegans, both the shape and size of male caudal appendages and the female prothorax evolved in strong evolutionary correlation, whereas in I. graellsii this association was restricted to shape. Reproductive structures evolved at significantly higher rates than wings, indicating greater evolutionary lability in traits directly involved in mating. Evolutionary model comparisons revealed contrasting dynamics between shape and size, suggesting that multiple processes contribute to trait divergence rather than a single dominant mechanism. Estimates of isolation by distance and gene flow revealed contrasting demographic contexts between species, with I. elegans showing more restricted gene flow than I. graellsii. Overall, our findings suggest that reproductive and non-reproductive traits differ in their evolutionary integration, rates, and dynamics, highlighting how trait-specific evolutionary patterns and demographic context contribute to morphological divergence in recently diverged taxa.

Insects are crucial for ecosystem functioning and provisioning services, yet the study of their decline is hampered by traditional monitoring systems. Airborne eDNA has the potential to help monitor the rapid changes insect communities are experiencing. Polyurethane foam passive air samplers (PUF‐PAS) are widely deployed to monitor environmental pollutants, yet their capacity to capture biological signals such as environmental DNA (eDNA) remains largely unexplored. Recent advances in airborne eDNA research create a timely opportunity to evaluate PUF‐PAS as a tool for biodiversity monitoring and to leverage existing global sampling networks for conservation. Focusing on insects, we assess whether PUF‐PAS can provide eDNA‐based biodiversity data comparable to those obtained with traditional sampling methods. We compared the taxonomic richness, community composition, and detection biases of PUF‐PAS to a conventional method for sampling flying insects, Malaise traps. We deployed both samplers across Montreal, Canada, during the entire flight season and collected 49 samples of each method. Insect communities were characterized at the order level using morphological identification (Malaise traps) and DNA metabarcoding (PUF‐PAS). Insect communities collected with both methods showed substantial overlap, with 11 insect orders detected by both methods; 3 were unique to Malaise traps and 1 to PUF‐PAS. On average, estimates of insect abundance from Malaise traps were strongly positively associated with PUF‐PAS detection probability and read counts. However, PUF‐PAS detection probability and read counts were best explained by Malaise trap counts measured several weeks prior and integrated over approximately 8 weeks, indicating a delayed biological signal. Our results suggest that PUF‐PAS is better suited for interannual monitoring of common insect taxa, particularly for detecting broad temporal trends. Given the availability of global passive air sampling infrastructure, this approach not only has strong potential for large‐scale biodiversity monitoring but also could foster interdisciplinary collaborations between environmental toxicologists and biodiversity scientists.

Hybridization outcomes often vary across space and time, yet the relative roles of demographic history and chromosomal differences in shaping introgression remain unclear. Here, we investigate three replicated hybrid zones between the damselflies Ischnura elegans and Ischnura graellsii across Spain to test whether genomic introgression patterns are repeatable across independently formed zones. Using genome-wide data, we combined demographic modeling, genomic cline, and functional annotation of introgressed loci. Demographic inference supported three independent secondary contact events of different ages: The South-east zone forming first (~207 years ago), followed by the North-west (~73.5 years) and North-central (~33 years) hybrid zones. Despite similar cline steepness across autosomes, asymmetric gene flow from I. graellsii into I. elegans was observed, with a low overlap of introgressed loci between zones. These loci were mainly associated with broad physiological and regulatory functions. In contrast, the X chromosome showed steeper clines, suggesting strong intrinsic genomic constraints. Together, demographic history explains geographic heterogeneity in introgression, whereas chromosome architecture imposes consistent constraints. These findings highlight how replicated hybrid zones can disentangle contingent versus repeatable genomic responses during early stages of speciation with gene flow.

Sexual bimaturism (SBM: differences between males and females in the timing of sexual maturity or adult emergence) is widespread in nature. Theoretical predictions suggest that SBM can evolve either directly by natural selection favoring males to emerge earlier to secure a female partner (direct selection hypothesis) or indirectly, by being physiologically coupled to other life history traits (indirect selection hypothesis), for example, sexual size dimorphisms (SSD). In insects, both processes lead frequently to males emerging earlier than females (protandry). Measuring the plasticity in the magnitude and direction of SBM across a gradient of larval environmental qualities can provide key insights into the underlying drivers of SBM. If SBM has been directly selected, the degree of protandry is expected to be independent of the environmental quality. Here, we measured the plasticity in SBM in the economically relevant black soldier fly (BSF; Hermetia illucens Linnaeus, 1758; Stratiomyidae: Hermetiinae) by exposing larvae to nutrient availability and humidity stress. Our results show that SBM can range between protandry and protogyny (females emerging earlier than males) depending on the environmental quality. Additionally, consistent with the indirect selection hypothesis, we found the degree of protandry to decrease as larval environmental quality improves. This ultimately leads to protogyny in optimal conditions. This result is consistent with the BSF life history traits and similar patterns observed in other dipterans. We suggest that SBM may be coupled to SSD in the BSF, thus leading to high plasticity that can shift between protandry and protogyny. The sensitivity of SBM to environmental quality suggests that it could be employed as a possible bioindicator of ecological stress in the field in species with high SBM plasticity.

Hybridisation outcomes often vary across space and time, yet the relative roles of demographic history and genomic architecture in shaping introgression remain unclear. Here, we investigate three replicated hybrid zones between the damselflies Ischnura elegans and Ischnura graellsii across Spain to test whether genomic introgression patterns are repeatable across independently formed zones. Using genome-wide data, we combined demographic modelling, genomic cline, and functional annotation of introgressed loci. Demographic inference supported three independent secondary contact events of different ages: The South-east zone forming first (∼207 years ago), followed by the North-west (∼73.5 years) and North-central (∼33 years) hybrid zones. Despite similar cline steepness across autosomes, asymmetric gene flow from I. graellsii into I. elegans was observed, with a low overlap of introgressed loci between zones. These loci were mainly associated with broad regulatory and transport-related functions in both hybrid zones, indicating repeatability at the level of gene function rather than gene identity. In contrast, the X chromosome showed steeper clines, suggesting strong intrinsic genomic constraints. Together, demographic history explains geographic heterogeneity in introgression, whereas chromosome architecture imposes consistent constraints. These findings highlight how replicated hybrid zones can disentangle contingent versus repeatable genomic responses during early stages of speciation with gene flow.

Theoretical and empirical studies of reinforcement have advanced our understanding of speciation, yet its role in polymorphic species remains understudied. Because morphs differ in behavior, morphology, and reproductive strategies, reinforcement may act unevenly among them, generating asymmetric reproductive isolation. We tested this prediction in the polymorphic damselflies Ischnura elegans and Ischnura graellsii, in which female morphs adopt alternative reproductive strategies. These species form two independent hybrid zones where reinforcement has strengthened mechanical isolation and driven reproductive character displacement in mating-related structures. We quantified five reproductive barriers across female morphs to evaluate how color polymorphism interacts with reinforcement. We found clear asymmetry between morphs: gynochrome females of both species showed reinforced mechanical isolation, whereas androchromes did not, consistent with their contrasting reproductive strategies. Additionally, gametic barriers evolved in opposite directions between species. Fertility isolation was reinforced in I. elegans, while oviposition and fertility barriers relaxed in I. graellsii, but symmetrically between female morphs, likely reflecting gene flow and purging of incompatibilities. Reinforcement strengthened reproductive isolation in a morph-specific manner, as pre-existing differences between female morphs influenced the likelihood of heterospecific mating and therefore the strength of selection against hybridization. Future work should examine whether these asymmetric dynamics generate cascading effects within species and contribute to morph-level diversification.

Pair of species with multiple hybrid zones provide powerful systems to examine how reproductive isolation and reinforcement may depend on ecological and demographic contexts. We conducted a comparative analysis of two hybrid zones between Ischnura elegans and Ischnura graellsii in North-central (NC) and North-western (NW) Spain to evaluate how differences in reproductive barriers shape patterns of hybridization and admixture. First, we quantified five prezygotic barriers in the NC hybrid zone—where no barrier estimates previously existed—and compared them with published data from the NW hybrid zone. Second, we conducted genomic analyses using 5,702 SNPs to assess genetic structure, differentiation, and diversity between species; and 381 SNPs with species-specific alleles to characterize hybrid classes and introgression across both regions. Reproductive isolation was strongly context dependent. Mechanical reinforcement acted in the same cross direction in both hybrid zones, but the NC hybrid zone also showed stronger gametic (fertility) isolation. Consequently, total prezygotic isolation was higher in the NC hybrid zone. These differences were also observed genomically: the NC hybrid zone exhibited limited and largely unidirectional introgression, whereas the NW hybrid zone showed more extensive admixture, bidirectional gene flow, and reduced interspecific differentiation, consistent with a longer or more sustained history of hybridization. Our results demonstrate that hybridization outcomes can differ markedly between hybrid zones involving the same pair of species, underscoring the importance of evaluating spatial variation in reproductive barriers and introgression to assess the presence, asymmetry, and repeatability of reinforcement, as well as the microevolutionary processes shaping hybrid zone structure.

Management of fecal waste from superabundant wildlife in urban areas is a key environmental and public health concern, yet even in developed countries, sustainable solutions that implement circular economy principles are still lacking. We tested the potential of black soldier fly (BSF) larvae for valorizing organic waste of the widespread Canada goose: converting droppings into larval protein while yielding frass fertilizer. Larvae were able to survive, develop, and degrade the goose feces. For instance, larvae degraded 56% of goose feces compared to 63% of a control diet. Sterilization of feces reduced the performance of larvae. We tested the fertilization properties of the insect frass on an aquatic plant (duckweed) and we found growth enhancement of 32% at 10 g·L ^-1 compared to a standard Hoagland’s media. Our results provide insights into how to sustainably manage urban fecal waste from overabundant species while producing protein and a nutrient-rich fertilizer for plants.