Higher evolutionary dynamics of gene copy number for Drosophila glue genes located near short repeat sequences.

BACKGROUND: During evolution, genes can experience duplications, losses, inversions and gene conversions. Why certain genes are more dynamic than others is poorly understood. Here we examine how several Sgs genes encoding glue proteins, which make up a bioadhesive that sticks the animal during metamorphosis, have evolved in Drosophila species. RESULTS: We examined high-quality genome assemblies of 24 Drosophila species to study the evolutionary dynamics of four glue genes that are present in D. melanogaster and are part of the same gene family - Sgs1, Sgs3, Sgs7 and Sgs8 - across approximately 30 millions of years. We annotated a total of 102 Sgs genes and grouped them into 4 subfamilies. We present here a new nomenclature for these Sgs genes based on protein sequence conservation, genomic location and presence/absence of internal repeats. Two types of glue genes were uncovered. The first category (Sgs1, Sgs3x, Sgs3e) showed a few gene losses but no duplication, no local inversion and no gene conversion. The second group (Sgs3b, Sgs7, Sgs8) exhibited multiple events of gene losses, gene duplications, local inversions and gene conversions. Our data suggest that the presence of short "new glue" genes near the genes of the latter group may have accelerated their dynamics. CONCLUSIONS: Our comparative analysis suggests that the evolutionary dynamics of glue genes is influenced by genomic context. Our molecular, phylogenetic and comparative analysis of the four glue genes Sgs1, Sgs3, Sgs7 and Sgs8 provides the foundation for investigating the role of the various glue genes during Drosophila life.

Predatory fireflies and their toxic firefly prey have evolved distinct toxin resistance strategies.

Toxic cardiotonic steroids (CTSs) act as a defense mechanism in many firefly species (Lampyridae) by inhibiting a crucial enzyme called Na+,K+-ATPase (NKA). Although most fireflies produce these toxins internally, species of the genus Photuris acquire them from a surprising source: predation on other fireflies. The contrasting physiology of toxin exposure and sequestration between Photuris and other firefly genera suggests that distinct strategies may be required to prevent self-intoxication. Our study demonstrates that both Photuris and their firefly prey have evolved highly resistant NKAs. Using an evolutionary analysis of the specific target of CTS (ATPα) in fireflies and gene editing in Drosophila, we find that the initial steps toward resistance were shared among Photuris and other firefly lineages. However, the Photuris lineage subsequently underwent multiple rounds of gene duplication and neofunctionalization, resulting in the development of ATPα paralogs that are differentially expressed and exhibit increasing resistance to CTS. By contrast, other firefly species have maintained a single copy. Our results implicate gene duplication as a facilitator in the transition of Photuris to its distinct ecological role as a predator of toxic firefly prey.

Predatory fireflies and their toxic firefly prey have evolved distinct toxin resistance strategies.

Toxic cardiotonic steroids (CTS) act as a defense mechanism in many firefly species (Lampyridae) by inhibiting a crucial enzyme called Na+,K+-ATPase (NKA). While most fireflies produce these toxins internally, species of the genus Photuris acquire them from a surprising source: predation on other fireflies. The contrasting physiology of toxin exposure and sequestration between Photuris and other firefly genera suggests that distinct strategies may be required to prevent self-intoxication. Our study demonstrates that both Photuris and their firefly prey have evolved highly-resistant NKAs. Using an evolutionary analysis of the specific target of CTS (ATPα) in fireflies, and gene-editing in Drosophila, we find that the initial steps towards resistance were shared among Photuris and other firefly lineages. However, the Photuris lineage subsequently underwent multiple rounds of gene duplication and neofunctionalization, resulting in the development of ATPα paralogs that are differentially expressed and exhibit increasing resistance to CTS. In contrast, other firefly species have maintained a single copy. Our results implicate gene duplication as a facilitator in the transition of Photuris to its distinct ecological role as predator of toxic firefly prey.

Glue Genes Are Subjected to Diverse Selective Forces during Drosophila Development.

Molecular evolutionary studies usually focus on genes with clear roles in adult fitness or on developmental genes expressed at multiple time points during the life of the organism. Here, we examine the evolutionary dynamics of Drosophila glue genes, a set of eight genes tasked with a singular primary function during a specific developmental stage: the production of glue that allows animal pupa to attach to a substrate for several days during metamorphosis. Using phenotypic assays and available data from transcriptomics, PacBio genomes, and sequence variation from global populations, we explore the selective forces acting on glue genes within the cosmopolitan Drosophila melanogaster species and its five closely related species, D. simulans, D. sechellia, D. mauritiana, D. yakuba, and D. teissieri. We observe a three-fold difference in glue adhesion between the least and the most adhesive D. melanogaster strain, indicating a strong genetic component to phenotypic variation. These eight glue genes are among the most highly expressed genes in salivary glands yet they display no notable codon bias. New copies of Sgs3 and Sgs7 are found in D. yakuba and D. teissieri with the Sgs3 coding sequence evolving rapidly after duplication in the D. yakuba branch. Multiple sites along the various glue genes appear to be constrained. Our population genetics analysis in D. melanogaster suggests signals of local adaptive evolution for Sgs3, Sgs5, and Sgs5bis and traces of selective sweeps for Sgs1, Sgs3, Sgs7, and Sgs8. Our work shows that stage-specific genes can be subjected to various dynamic evolutionary forces.

Drosophila glue protects from predation.

Animals can be permanently attached to a substrate in terrestrial environments at certain stages of their development. Pupa adhesion has evolved multiple times in insects and is thought to maintain the animal in a place where it is not detectable by predators. Here, we investigate whether pupa adhesion in Drosophila can also protect the animal by preventing potential predators from detaching the pupa. We measured the adhesion of Drosophila species sampled from the same area and found that pupa adhesion varies among species, which can be explained by different glue production strategies. Then, we compared attached and manually detached pupae in both field and laboratory assays to investigate the role of pupa adhesion to prevent predation. First, we found that attached pupae remain onsite 30% more than detached pupae in the field after 3 days, probably because they are less predated. Second, we observed that attached pupae are less efficiently predated by ants in the laboratory: they are not carried back to the ant nest and more ants are needed to consume them onsite. Our results show that pupa adhesion can prevent the animal from being taken away by predators and is crucial for Drosophila fly survival.

The glue produced by Drosophila melanogaster for pupa adhesion is universal.

Insects produce a variety of adhesives for diverse functions such as locomotion, mating, and egg or pupal anchorage to substrates. Although they are important for the biology of organisms and potentially represent a great resource for developing new materials, insect adhesives have been little studied so far. Here, we examined the adhesive properties of the larval glue of Drosophila melanogaster This glue is made of glycosylated proteins and allows the animal to adhere to a substrate during metamorphosis. We designed an adhesion test to measure the pull-off force required to detach a pupa from a substrate and to evaluate the contact area covered by the glue. We found that the pupa adheres with similar forces to a variety of substrates (with distinct roughness, hydrophilic and charge properties). We obtained an average pull-off force of 217 mN, corresponding to 15,500 times the weight of a pupa and an adhesion strength of 137-244 kPa. Surprisingly, the pull-off forces did not depend on the contact area. Our study paves the way for a genetic dissection of the components of D. melanogaster glue that confer its particular adhesive properties.

Quantifying male and female pheromone-based mate choice in Caenorhabditis nematodes using a novel microfluidic technique.

Pheromone cues are an important component of intersexual communication, particularly in regards to mate choice. Caenorhabditis nematodes predominant rely on pheromone production for mate finding and mate choice. Here we describe a new microfluidic paradigm for studying mate choice in nematodes. Specifically, the Pheromone Arena allows for a constant flow of odorants, including pheromones and other small molecules, to be passed in real time from signaling worms to those making a choice without any physical contact. We validated this microfluidic paradigm by corroborating previous studies in showing that virgin C. remanei and C. elegans males have a strong preference for virgin females over mated ones. Moreover, our results suggest that the strength of attraction is an additive effect of male receptivity and female signal production. We also explicitly examine female choice and find that females are more attracted to virgin males. However, a female's mate choice is strongly dependent on her mating status.