Candidate genes involved in cuticular hydrocarbon differentiation between cryptic, parabiotic ant species

Abstract

Insect cuticular hydrocarbons (CHCs) are highly diverse and have multiple functions, including communication and waterproofing. CHC profiles form species-specific, complex blends of up to 150 compounds. Especially in ants, even closely related species can have largely different profiles, raising the question how CHC differences are mirrored in the regulation of biosynthetic pathways. The neotropical ants Crematogaster levior and Camponotus femoratus both consist of two cryptic species each that are morphologically similar, but express strongly different CHC profiles. This is ideal to study the molecular basis of CHC differences. We thus investigated gene expression differences in fat-body transcriptomes of these ants. Despite common garden conditions, we found several thousand differentially expressed transcripts within each cryptic species pair. Many of these were related to metabolic processes, probably accounting for physiological differences. Moreover, we identified candidate genes from five gene families involved in CHC biosynthesis. By assigning candidate transcripts to orthologs in Drosophila, we inferred which CHCs might be influenced by differential gene expression. Expression of these candidate genes was often mirrored in the CHC profiles. For example, Cr. levior A, which has longer CHCs than its cryptic sister species, had a higher expression of elongases and fatty acyl- CoA reductases. This study is one of the first to identify CHC candidate genes in ants and will provide a basis for further research on the genetic basis of CHC biosynthesis.

Chemical and population genetic analysis show no evidence of ecotype formation in a European population of the parasitoid wasp Nasonia vitripennis

“…CHC differences might also occur due to assortative mating and have been found to be correlated with speciation events in other insects (Schwander et al, 2013;Chung and Carroll, 2015). Moreover, CHC profiles have frequently been found as the first and most characteristic phenotypic traits to diverge between populations and evolutionarily young species pairs (Espelie et al, 1990;Raychoudhury et al, 2010;Sprenger et al, 2021). Therefore, it is surprising that we could not detect any congruent CHC divergence separating the two postulated N. vitripennis ecotypes.…”

“…CHC profiles have repeatedly been demonstrated to diverge rapidly in populations according to different ecological conditions (Menzel et al, 2017;Menzel et al, 2018;Hartke et al, 2019). Furthermore, CHC profiles have the potential to be utilized as chemotaxonomic traits to successfully discriminate otherwise indistinguishable sympatric populations of a single species (Takahashi et al, 2001;Everaerts et al, 2008) or recently diverged sister species (Finck et al, 2016;Sprenger et al, 2021). Notably, CHC profiles were the most apparent phenotypic traits clearly distinguishing the two most recently diverged species of the Nasonia genus, N. giraulti and N. oneida (Raychoudhury et al, 2010;Werren et al, 2010).…”

Chemical and transcriptomic diversity do not correlate with ascending levels of social complexity in the insect order Blattodea

“…The assessment of transcript counts as approximation of the actual genomic repertoire for CHC biosynthesis genes naturally has its limits and will remain speculative until targeted knockdown studies confirm the actual functions of the transcripts as well as their underlying genes. However, analyzing the abundance of unique transcripts per ortholog allows valuable insights into functional diversity potentially exceeding the information contained within whole-genome sequences (He et al 2021;Sprenger et al 2021). Correlating transcriptomic diversity directly with CHC profile variation has been attempted surprisingly rarely despite its potential to approximate the genetic control of CHC variation more accurately, as it has repeatedly been shown that the same genotype can produce different CHC profiles (Holze et al 2021;Sprenger et al 2021).…”

“…However, analyzing the abundance of unique transcripts per ortholog allows valuable insights into functional diversity potentially exceeding the information contained within whole-genome sequences (He et al 2021;Sprenger et al 2021). Correlating transcriptomic diversity directly with CHC profile variation has been attempted surprisingly rarely despite its potential to approximate the genetic control of CHC variation more accurately, as it has repeatedly been shown that the same genotype can produce different CHC profiles (Holze et al 2021;Sprenger et al 2021). Thus, our findings constitute promising first steps for future studies with the potential to corroborate our transcriptomic assessment with target gene counts once further genomic resources become available.…”

Cuticular Hydrocarbon Profiling Reveals Chemotaxonomic Diversity among Gonipterini weevils (Coleoptera: Curculionidae)

“…However, the emergence of cuticular hydrocarbon (CHC) profiling has emerged as a useful chemotaxonomic tool over the past few decades [4]. These compounds are endogenously synthesized by nearly all insects and exported to the cuticle [5,6], with one of their major functions being to mediate communication with other insects. Consequently, there is a wide range of diversity in CHC profiles, which is reflective of the genetic diversity of the species in question.…”