Evolution of physiological dormancy multiple times in Melastomataceae from Neotropical montane vegetation

Abstract

We investigated seed dormancy among species of Melastomataceae from Neotropical montane vegetation of Brazil. Four out of 50 studied species had dormant seeds:Miconia corallina(Miconieae), Tibouchina cardinalis(Melastomeae), Comolia sertularia(Melastomeae) andChaetostoma armatum(Microlicieae). For these four species, germinability of seeds collected in different years was always < 10% and the percentages of embryoless seeds and non-viable embryos were both insufficient to explain low or null germinability. This is the first unequivocal report of seed dormancy in tropical Melastomataceae. The production of seeds with permeable seed coats and fully developed, differentiated embryos indicates the occurrence of physiological dormancy. The reconstructed phylogenetic tree of the 50 species suggests that physiological dormancy evolved multiple times during the evolutionary history of Melastomataceae in this vegetation. Physiological dormancy evolved in species and populations associated with xeric microhabitats, where seeds are dispersed in unfavourable conditions for establishment. Therefore, drought-induced mortality may have been a strong selective pressure favouring the evolution of physiological dormancy in Melastomataceae. We argue that dormancy may have been independently selected in other lineages of Cerrado plants colonizing xeric microhabitats and dispersing seeds at the end of the rainy season. The contributions of our data to the understanding of seed dormancy in tropical montane vegetation are discussed.

Effects of gut passage on the germination of seeds ingested by didelphid marsupials in a neotropical savanna

“…These germination strategies were also observed for other seeds dispersed by didelphids in the neotropical region (Cáceres 2002;Cáceres & Monteiro-Filho 2007;Cantor et al 2010;Cáceres & Lessa 2012) and reinforce the importance of seasonal soil water deficits in determining the probability of germination (Cáceres & Monteiro-Filho 2007) in environments such as the cerrado. The consumed seeds showed different germination times and, in a general way, germination was delayed until periods of more favorable environmental conditions (see Cáceres 2002;Thompson & Ooi 2010;Silveira et al 2012a).…”

Sowing seeds for the future: the need for establishing protocols for the study of seed dormancy

“…Intraspecific variation in the level of seed dormancy is common among Brazilian species (Lacerda et al, 2004;Silveira et al 2012), and the question posed is no longer whether a species is dormant or not. Rather, we should be asking ourselves if individuals or populations present dormant seeds and what are the conditions that have favoured the evolution of dormancy in these demes.…”

“…Therefore, testing germination under a wide range of physical conditions is especially recommended (see Finch-Savage & Leubner-Metzger 2006 for a discussion on light and dormancy). Second, many species have high proportions of embryoless seeds, including Melastomataceae (Simão et al 2007;Silveira et al, 2012), Asteraceae (Velten & Garcia 2005;Galastri & Oliveira 2010;Le Stradic 2012) and Poaceae (Le Stradic 2012). The proportion of embryoless seeds can be over 95% (Gupta & Murty 1986).…”

“…To determine if diaspores are water impermeable, they should be weighed before and after a period of incubation on a wet substrate or of soaking in tap water (Baskin et al 2006). Periods of incubation may range from 8 h to 72 h. Appropriate statistics must be run to determine whether there are significant differences between the seed mass of dried and soaked seeds (Silveira et al 2012;Le Stradic 2012). The finding of seed/ fruit coat permeability supports the notion of physical or combinational dormancy and the use of scarification can distinguish between them (Fig.…”

“…Detailed descriptions of embryo anatomy may prove helpful but are not strictly needed. To further assess details on embryo anatomy, routine anatomical procedures can be carried out (see Silveira et al 2012 and references therein), but simple seed dissection procedures for evaluating embryo growth (Silva et al 2007) or to confirm that seeds have fully developed/differentiated embryos are sufficient for assigning morphological or morphophysiological dormancy (Fig. 1).…”