Cryptic species within the cosmopolitan desiccation-tolerant moss Grimmia laevigata

Abstract

The common cushion moss Grimmia laevigata (Bridel) Bridel grows on bare rock in a broad range of environments on every continent except Antarctica. As such, it must harbor adaptations to a remarkably broad set of environmental stresses, the extremes of which can include very high temperatures, prolonged nearly complete desiccation, and high ultraviolet B (UVB) exposure. Yet, like many mosses, G. laevigata shows very little morphological variability across its cosmopolitan range. This presents an evolutionary puzzle, the solution to which lies in understanding the phylogeographic structure of this morphologically simple organism. Here we report the results of an analysis of amplified fragment length polymorphisms (AFLPs) in G. laevigata, focusing on individuals from the California Floristic Province. We found evidence that populations within California constitute two distinct geographically overlapping cryptic species. Each clade harbors multiple private alleles, indicating they have been genetically isolated for some time. We suggest that the existence of cryptic species within G. laevigata, in combination with its life history, growth habits, and extreme desiccation tolerance, makes this moss an ideal research tool and a candidate for a biological indicator of climate change and pollution.

Fig. 1.

Strict consensus cladogram showing maximum-parsimony relationships among the G. laevigata samples. P. gardneri and G. ovalis were used to root trees. Numbers above branches are boostrap values. Individuals are labeled with region and sample identification in parentheses, corresponding to Table 1.

Fig. 2.

Principal coordinates analysis of Jaccard's distance among the 46 Grimmia individuals. The first two axes explain 31.5% of total variation.

Fig. 3.

Map of collection sites of the 44 G. laevigata individuals.

Fig. 4.

Isolation-by-distance analysis among G. laevigata individuals. (a) All samples analyzed together. (b) Clade 1 analyzed separately. (c) Clade 2 analyzed separately. Each point shows Jaccard's index of genetic distance between a pair of individuals and the geographic distance between that pair.