RESUMEN
Lichens can either disperse sexually through fungal spores or asexually through vegetative propagules and fragmentation. Understanding how genetic variation in lichens is distributed across a landscape can be useful to infer dispersal and establishment events in space and time as well as the conditions needed for this establishment. Most studies have sampled lichens across large spatial distances on the order of hundreds of kilometers, while here we sequence the internal transcribed spacer (ITS) for 113 samples of three Peltigera species sampling at a variety of small spatial scales. The maximum distance between sampled lichens was 3.7 km and minimum distance was approximately 20 cm. We find significant amounts of genetic diversity across all three species. For P. praetextata, two out of the three most common ITS genotypes exhibit spatial autocorrelation supporting short-range dispersal. Using rarefaction we estimate that all ITS genotypes in our sampling area have been found for P. praetextata and P. evansiana, but not P. canina. Comparing our results with other ITS data in the literature provides evidence for global dispersal for at least one sequence followed by the evolution of endemic haplotypes with wide dispersal and rare haplotypes with more local dispersal.
RESUMEN
The Drosophila sex comb (SC) has been hailed as a powerful tool for integrative studies in development, evolution, and behavior, but its ontogeny is poorly understood, even in the model organism Drosophila melanogaster. Using 4D live imaging and other techniques, we carried out a detailed analysis of the cellular events that take place during the development of the SC. We showed that the comb and other contiguous bristle formations assemble from noncontiguous precursor cells, which join together through intercalation. Most of the rotation of the SC (which has a longitudinal orientation in D. melanogaster but is initially transverse) occurs after this stage, when the structure is a single unit. We have provided evidence that male-specific convergent extension through cell rearrangement is responsible for both this rotation and another sexually dimorphic bristle trait. Contiguous bristle formations act as barriers to cell movement within the epithelium, and we demonstrated that a particularly rapid rotation of the proximal region of the comb is associated with the presence of a constricted area between a portion of the SC and a transverse row of contiguous bristle precursors. Our results suggest that the cell dynamics in the neighborhood of the SC may have biased its evolution.
Asunto(s)
Drosophila melanogaster/fisiología , Caracteres Sexuales , Animales , Evolución Biológica , Evolución Molecular , Extremidades , Femenino , Regulación del Desarrollo de la Expresión Génica , Proteínas Fluorescentes Verdes/metabolismo , Masculino , Microscopía Confocal/métodos , Microscopía Electrónica de Rastreo , Morfogénesis , FenotipoRESUMEN
The most complex and diverse secondary sexual character in Drosophila is the sex comb (SC), an arrangement of modified bristles on the forelegs of a subclade of male fruit flies. We examined SC formation in six representative nonmodel fruit fly species, in an effort to understand how the variation in comb patterning arises. We first compared SC development in two species with relatively small combs, Drosophila takahashii, where the SCs remain approximately transverse, and Drosophila biarmipes, where two rows of SC teeth rotate and move in an anterior direction relative to other bristle landmarks. We then analyzed comb ontogeny in species with prominent extended SCs parallel to the proximodistal axis, including Drosophila ficusphila and species of the montium subgroup. Our study allowed us to identify two general methods of generating longitudinal combs on the tarsus, and we showed that a montium subgroup species (Drosophila nikananu) with a comb convergently similar in size, orientation and position to the model organism Drosophila melanogaster, forms its SC through a different developmental mechanism. We also found that the protein product of the leg patterning gene, dachshund (dac), is strongly reduced in the SC in all species, but not in other bristles. Our results suggest that an apparent constraint on SC position in the adult may be attributable to at least two different lineage-specific developmental processes, although external forces could also play a role.