Distribution and ecological segregation on regional and microgeographic scales of the diploidCentaurea asperaL., the tetraploidC. seridisL., and their triploid hybrids (Compositae)

Although polyploidy is considered a ubiquitous process in plants, the establishment of new polyploid species may be hindered by ecological competition with parental diploid taxa. In such cases, the adaptive processes that result in the ecological divergence of diploids and polyploids can lead to their co-existence. In contrast, non-adaptive processes can lead to the co-existence of diploids and polyploids or to differentiated distributions, particularly when the minority cytotype disadvantage effect comes into play. Although large-scale studies of cytotype distributions have been widely conducted, the segregation of sympatric cytotypes on fine scales has been poorly studied. We analysed the spatial distribution and ecological requirements of the tetraploidCentaurea seridisand the diploidCentaurea asperain east Spain on a large scale, and also microspatially in contact zones where both species hybridise and give rise to sterile triploid hybrids. On the fine scale, the position of eachCentaureaindividual was recorded along with soil parameters, accompanying species cover and plant richness. On the east Spanish coast, a slight latitudinal gradient was found. TetraploidC. seridisindividuals were located northerly and diploidC. asperaindividuals southerly. Tetraploids were found only in the habitats with strong anthropogenic disturbance. In disturbed locations with well-developed semi-fixed or fixed dunes, diploids and tetraploids could co-exist and hybridise. However, on a fine scale, although taxa were spatially segregated in contact zones, they were not ecologically differentiated. This finding suggests the existence of non-adaptive processes that have led to their co-existence. Triploid hybrids were closer to diploid allogamous mothers (C. aspera) than to tetraploid autogamous fathers (C. seridis). This may result in a better ability to compete for space in the tetraploid minor cytotype, which might facilitate its long-term persistence.

A new sympatric region for distinct karyotypic forms of Hoplias malabaricus (Pisces, Erythrinidae)

Specimens of Hoplias malabaricus from Lagoa Carioca, an isolated lake of the Rio Doce State Park (state of Minas Gerais, Brazil), were cytogenetically studied. The diploid number was found to be constant, i.e., 2n = 42 chromosomes, although two karyotypic forms were found: karyotype A, characterized by 22M + 20SM chromosomes, observed only in a male specimen, and karyotype B, characterized by 24M + 16SM + 2ST and 24M + 17SM + 1ST chromosomes in female and male specimens, respectively. This sex difference found in karyotype B is related to an XX/XY sex chromosome system. Another female specimen of H. malabaricus, also carrying karyotype A, had previously been found in the same lake. The available data indicate that two sympatric cytotypes of H. malabaricus exist in the Lagoa Carioca, with cytotype A occurring at a lower frequency and differing from cytotype B by undifferentiated sex chromosomes.