Project description:Non-random female mating preferences may contribute to the maintenance of phenotypic variation in color polymorphic species. However, the effect of female preference depends on the types of male traits used as signals by receptive females. If preference signals derive from discrete male traits (i.e., morph-specific), female preferences may rapidly fix to a morph. However, female preference signals may also include condition-dependent male traits. In this scenario, female preference may differ depending on the social context (i.e., male morph availability). Male tree lizards (Urosaurus ornatus) exhibit a dewlap color polymorphism that covaries with mating behavior. Blue morph males are aggressive and defend territories, yellow males are less aggressive and defend smaller territories, and orange males are typically nomadic. Female U. ornatus are also polymorphic in dewlap color, but the covariation between dewlap color and female behavior is unknown. We performed an experiment to determine how female mate choice depends on the visual and chemical signals produced by males. We also tested whether female morphs differ in their preferences for these signals. Female preferences involved both male dewlap color and size of the ventral color patch. However, the female morphs responded to these signals differently and depended on the choice between the types of male morphs. Our experiment revealed that females may be capable of distinguishing among the male morphs using chemical signals alone. Yellow females exhibit preferences based on both chemical and visual signals, which may be a strategy to avoid ultra-dominant males. In contrast, orange females may prefer dominant males. We conclude that female U. ornatus morphs differ in mating behavior. Our findings also provide evidence for a chemical polymorphism among male lizards in femoral pore secretions.
Project description:Urosaurus nigricaudus is a phrynosomatid lizard endemic to the Baja California Peninsula in Mexico. This work presents a chromosome-level genome assembly and annotation from a male individual. We used PacBio long reads and HiRise scaffolding to generate a high-quality genomic assembly of 1.87 Gb distributed in 327 scaffolds, with an N50 of 279 Mb and an L50 of 3. Approximately 98.4% of the genome is contained in 14 scaffolds, with 6 large scaffolds (334-127 Mb) representing macrochromosomes and 8 small scaffolds (63-22 Mb) representing microchromosomes. Using standard gene modeling and transcriptomic data, we predicted 17,902 protein-coding genes on the genome. The repeat content is characterized by a large proportion of long interspersed nuclear elements that are relatively old. Synteny analysis revealed some microchromosomes with high repeat content are more prone to rearrangements but that both macro- and microchromosomes are well conserved across reptiles. We identified scaffold 14 as the X chromosome. This microchromosome presents perfect dosage compensation where the single X of males has the same expression levels as two X chromosomes in females. Finally, we estimated the effective population size for U. nigricaudus was extremely low, which may reflect a reduction in polymorphism related to it becoming a peninsular endemic.
Project description:Hybrids can experience genetic incompatibilities that lead to cellular dysfunction and infertility. Previous analyses of mitochondrial function in the lizards Urosaurus graciosus and Urosaurus ornatus found that hybrids, which had introgressed mtDNA, experienced higher ATP production which increases reactive oxygen species (ROS) production, one of the main causes of damage to DNA. Hybrid populations of these lizards have persisted so we predicted they may have mechanisms for protecting their DNA from damage. To test this, we exposed liver cells of these lizards to hydrogen peroxide, a source of ROS, and compared DNA damage using single-cell gel electrophoresis. Hybrid cells showed significantly less DNA damage. We then examined potential mechanisms to explain this result by comparing melanin content of livers and expression levels of antioxidant genes. If functioning to deal with ROS, these should be expressed higher in hybrids. Melanin content of livers was highly variable among U. graciosus individuals and therefore not highest in hybrids as expected. Eighteen antioxidant genes showed significant differential expression but were not expressed consistently higher in hybrids. The overall gene expression profiles of hybrids and U. graciosus were very similar while that of the mtDNA donor species, U. ornatus, was highly divergent from both. Three antioxidant genes with different expression levels in hybrids and that warrant further study were SOD2, SOD3, and PRDX2. These results show how species can compensate for mtDNA introgression and highlight the complexity of genetic interactions encountered when closely related species exchange genetic material in zones of secondary contact.