Microchromosome BAC-FISH Reveals Different Patterns of Genome Organization in Three Charadriiformes Species

SIMPLE SUMMARY: Numerous tiny (micro)chromosomes are a characteristic feature associated with birds, being found in smaller numbers in other organisms and absent in many, such as mammals. Although microchromosomes constitute a large portion of the genome in birds, data on them pertaining to comparative studies between birds are still scarce. This is the case in shorebirds (Charadriiformes), a group with a great variety of species. The aim of this study was to provide insight regarding the evolution of the microchromosomes of three species of shorebirds—the red knot (Calidris canutus), the wattled jacana (Jacana jacana), and the southern lapwing (Vanellus chilensis). The experiments are referred to as cross-species fluorescence in situ hybridization (FISH) mapping using probes called bacterial artificial chromosomes (or BACs), two (one labelled in red and one labelled in green) for every microchromosome. The results thus appear as the microchrochromosome with one green and one red end, revealing different patterns of organization over evolutionary time. In the red knot, they fuse together, but in the southern lapwing, they hardly change. We also described a new chromosome number for the red knot (92 in total). In conclusion, this study contributed to the understanding of microchromosomes organization and evolution of three shorebird species. ABSTRACT: Microchromosomes, once considered unimportant elements of the genome, represent fundamental building blocks of bird karyotypes. Shorebirds (Charadriiformes) comprise a wide variety of approximately 390 species and are considered a valuable model group for biological studies. Despite this variety, cytogenetic analysis is still very scarce in this bird order. Thus, the aim of this study was to provide insight into the Charadriiformes karyotype, with emphasis on microchromosome evolution in three species of shorebirds—Calidris canutus, Jacana jacana, and Vanellus chilensis—combining classical and molecular approaches. Cross-species FISH mapping applied two BAC probes for each microchromosome, GGA10–28 (except GGA16). The experiments revealed different patterns of microchromosome organization in the species investigated. Hence, while in C. canutus, we found two microchromosomes involved in chromosome fusions, they were present as single pairs in V. chilensis. We also described a new chromosome number for C. canutus (2n = 92). Hence, this study contributed to the understanding of genome organization and evolution of three shorebird species.