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

Abstract

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 tetraploid Centaurea seridis and the diploid Centaurea aspera in 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 each Centaurea individual was recorded along with soil parameters, accompanying species cover and plant richness. On the east Spanish coast, a slight latitudinal gradient was found. Tetraploid C. seridis individuals were located northerly and diploid C. aspera individuals 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.

Intra- and Inter-Specific Crosses among Centaurea aspera L. (Asteraceae) Polyploid Relatives—Influences on Distribution and Polyploid Establishment

“…The production of unreduced gametes has been proven heritable, governed by a few genes, and increasing with environmental stress, such as heat, frost, water deficit, and herbivory [ 8 , 35 , 36 ]. This is in accordance with the higher frequency of polyploids found in habitats affected by climate fluctuations and disruptions [ 37 , 38 , 39 ]. Some studies pointed out that polyploid species are over-represented in previously glaciated regions, while diploids are more frequent in disjunct refugial areas [ 40 , 41 ].…”

“…Our results showed that the allotetraploid C. seridis produces almost twice the number of cypselae in the intra-specific crosses compared to C. aspera and C. gentilii . It is a bigger hairier plant that provides greater adaptability to coastal sandy habitats [ 32 , 38 ]. In the contact zones with C. aspera , asymmetric hybridization, along with the short distance dispersal of the hybrid cypselae, produces a differentiated microscale distribution with the sterile hybrid closer to the mother C. aspera [ 38 ].…”

“…It is a bigger hairier plant that provides greater adaptability to coastal sandy habitats [ 32 , 38 ]. In the contact zones with C. aspera , asymmetric hybridization, along with the short distance dispersal of the hybrid cypselae, produces a differentiated microscale distribution with the sterile hybrid closer to the mother C. aspera [ 38 ]. All these characteristics surely favored the initial establishment and competition of C. seridis in sympatry with its progenitors.…”

“…The Centaurea aspera L. polyploid complex has long since been studied, and it is mainly distributed in coastal habitats of Spain and Morocco. [ 32 , 38 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. What makes the C. aspera polyploid complex so interesting is that it is made up of natural populations of the parental diploid ( C. aspera L. 2x = 22), an allotetraploid ( C. seridis L. 4x = 44) and an autotetraploid ( C. gentilii Braun-Blanq.…”

Fitness of an allopolyploid rupicolous fern compared with its diploid progenitors: from sporogenesis to sporophyte formation

“…There is strong empirical evidence that minority cytotype exclusion operates in nature as a consequence of hybrid sterility (Husband, ). However, not only is polyploid speciation ubiquitous in plants, but also polyploids and diploid parents frequently form mixed populations (Garmendia et al., ). Evolutionary models have identified several factors that can enhance the establishment and persistence of polyploids among their diploid parents, such as higher relative fitness of polyploids (Felber, ), non‐random mating between cytotypes (Rausch and Morgan, ), and niche differentiation (Rodríguez, ).…”