Caenorhabditis tropicalis
"Caenorhabditis tropicalis" is a species of "Caenorhabditis" nematodes, belonging to the "Elegans" super-group and "Elegans" group within the genus. It is a close relative of "C. wallacei." "C. tropicalis" is collected frequently in tropical South America, Caribbean islands, and various islands in the Indian and Pacific Oceans from rotting fruit, flowers and stems. "C. tropicalis" was referred to as “"C." sp. 11” prior to 2014. Anatomy. The mean body lengths of adult hermaphroditic and adult male "C. tropicalis" were calculated as 1378.63µm and 992.85µm, respectively, making "C. tropicalis" males and hermaphrodites on average larger than  other hermaphroditic species like "C. elegans" and "C. briggsae". Spicule shape. The spicules of "C. tropicalis" males consist of a long, slender, pointed, and simple morphology, which is a common feature among Caenorhabditis species outside of the Elegans super-group (with the exception of "C. japonica" and "C. afra"). Reproduction. "C. tropicalis" demonstrates a hermaphroditic mode of reproduction. Similar to "C. elegans" and "C. briggsae", androdioecious populations of "C. tropicalis" are made up of protandrous hermaphrodites (XX sex chromosome karyotype) and X0 males. These three species are not each other's closest relatives, supporting the independent evolutionary origins of hermaphroditism  and androdioecy. The self-fertile hermaphroditic reproductive strategy of these species is an example of convergent evolution. Ecology. "C. tropicalis" was first discovered from La Reunion island in the Indian Ocean in 2008, with subsequent collection in Puerto Rico and Cape Verde Islands in the Atlantic Ocean, French Guiana and Brazil in South America, and Hawaii in the Pacific Ocean. "C. tropicalis" has only been sampled from tropical regions thus far. It is one of the most commonly-sampled "Caenorhabditis" species in the Nouragues Nature Reserve of French Guiana, where it has been isolated both in litter samples and from  rotting fruits and flowers. Like other "Caenorhabditis" species found in the tropical rainforest of French Guiana, "C. tropicalis" is commonly found among rotting flower substrates. This species demonstrates a preferential association with rotting flowers in earlier stages of decay, indicated by a decrease in association with flowers in later stages of decay. "C. tropicalis" has shown inter-species associations with Nematocida major, an intracellular pathogen that has also been observed to associate with "C. elegans" and "C. briggsae", two other hermaphroditic "Caenorhabditis" nematode species. N. major infections of these nematodes have only been observed in tropical regions even though "C.  elegans" is predominantly found in temperate regions. Genetics. The genome of "C. tropicalis" reference strain JU1373 consists of around 79.32 million base pairs and 22,326 protein coding genes. These genome characteristics make it shorter than the "C. elegans" genome, which consists of around 100.29 million base pairs and 20,326 protein coding genes. Like all known "Caenorhabditis" species, the genome of "C. tropicalis" is partitioned into six chromosomes (five autosomes and one “X” sex chromosome). Outbreeding Depression. Like the other Androdioecious Caenorhabditis species, "C. tropicalis" demonstrates outbreeding depression mediated by Medea like elements, which can result in lethality in "C. tropicalis  offspring, which results in smaller population sizes, it is likely due to this why C. tropicalis" faces an evolutionary pressure to demonstrate high rates of inbreeding. Crosses between strains of "C. tropicalis" isolated from different locations resulted in a higher frequency of defective offspring in comparison to crosses between strains of "C. tropicalis" from the same location. High inbreeding rates in "C. tropicalis" has subsequently resulted in a significant decrease in genomic diversity in this species compared to other "Caenorhabditis" nematodes. "C. tropicalis", along with "C. briggsae" and "C. elegans", the other two hermaphroditic "Caenorhabditis" species demonstrate 20-40% smaller  genome sizes compared to gonochoristic or male-female "Caenorhabditis" species.