Abstract
The harsh climatic conditions and paucity of potential pollinators on Southern Ocean Islands (SOIs; latitude 46°S-55°S) lead to the expectation that anemophily or self-fertilization are the dominant modes of plant sexual reproduction. However, at least some species have showy inflorescences suggesting biotic pollination or dimorphic breeding systems necessitating cross-pollination. This study investigates whether anemophily and self-compatibility are common on SOIs, whether species or genera with these traits are more widespread or frequent at higher latitudes, and whether gender dimorphy is correlated with anemophily, as might occur if reliance on pollinators was a disadvantage. Of the 321 flowering plant species in the SOI region, 34.3 % possessed floral traits consistent with anemophily. Compatibility information was located for 94 potentially self-fertilizing species, of which 92.6 % were recorded as partially or fully self-compatible. Dioecy occurred in 7.1 % of species overall and up to 10.2 % of island floras, but has not clearly arisen in situ. Gynodioecy occurred in 3.4 % of species. The frequency of anemophily and gender dimorphy did not differ between the SOI flora and southern hemisphere temperate reference floras. At the species level, gender dimorphy was positively associated with fleshy fruit, but at the genus level it was associated with occurrence in New Zealand and a reduced regional distribution. Anemophily was more prevalent in genera occurring on subantarctic islands and the proportion of species with floral traits suggestive of biotic pollination was significantly higher on climatically milder, cool temperate islands. These results support the contention that reliance on biotic pollinators has constrained the distribution of species on SOIs; however, it is also clear that the reproductive biology of few SOI species has been studied in situ and many species likely employ a mixed mating strategy combining biotic pollination with self-fertilization.
Highlights
Isolated islands provide an unparalleled opportunity to study evolutionary processes in plants (Carlquist 1977; Lloyd 1985; Sakai et al 1995; Grant 1998; Losos and Ricklefs 2009)
Islands are associated with a high incidence of dioecy (Carlquist 1977; Bawa 1982; Sakai et al 1995; Barrett 1998; Webb et al 1999; see Table 1 for breeding system terminologies), possibly due to selection for mechanisms that reduce the likelihood of inbreeding depression, as well as the well-known correlation between dioecy and fleshy fruits, which could make long-distance dispersal more likely (Bawa 1982; Sakai et al 1995; Sakai and Weller 1999; Webb et al 1999)
Very little experimental data exist concerning the reproductive ecology of Southern Ocean Islands (SOIs) plants in situ
Summary
Isolated islands provide an unparalleled opportunity to study evolutionary processes in plants (Carlquist 1977; Lloyd 1985; Sakai et al 1995; Grant 1998; Losos and Ricklefs 2009). Island plants tend to have smaller, less brightly coloured floral displays, lower flower visitation rates and a greater incidence of anemophily (wind pollination) (Carlquist 1977; Inoue et al 1995; Barrett 1998). Despite the importance of islands in understanding these evolutionary processes in plants, plant reproductive traits have still been investigated in remarkably few island floras and complete data are still lacking even for well-studied islands (Bernardello et al 2001; Newstrom and Robertson 2005; Chamorro et al 2012)
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