LIFE-HISTORY VARIATION IN MOSSES - WATER RELATIONS, SIZE AND PHYLOGENY

We evaluate the influences of gametophyte size, taxonomic affiliation (as an indicator of phylogenetic relationship), and water relations on variation and covariation of five life history traits among 335 moss species representing the orders Funariales, Polytrichales. and Pottial es. Size effects, though statistically significant, account for a rela tively small proportion of the variation in most life history traits. Canonical Correlation Analyses, conducted across all species as well a s within orders and larger Families, reveal significant relationships between patterns of covariation in life history traits and variation i n morpho-anatomical traits associated with water relations. Water rela tions account for 40-50% of life history variation depending on taxono mic group. but patterns of relationships between the two sets of varia bles are broadly similar, irrespective of the taxonomic group in which they were examined. The first water relations variate is a gradient d escribing water uptake/retention capacity. The life history variate as sociated with this is an axis that arranges species from those that ar e monoicous, short-lived and produce few large spores to those having the opposite suite of traits. The second water relations variate repre sents an endo-ectohydric gradient, which correlates with a life histor y variate describing differential investment in spores as a function o f life expectancy. We used Nested Analyses of Variance and Covariance to partition variance in the life history traits into taxonomic compon ents and evaluate whether size and water relations differences among p articular groups mediate apparent taxonomic effects. Generic influence s on all traits are strong, and independent of size and water relation s effects; together, genus and water relations account for >50% of the variation in each of the life history traits considered. Apparent ord inal effects largely disappear after adjustment for size and water rel ations, while substantial family level effects exist for spore number and spore size. Variation among species within genera is modest. These results suggest that most of the diversification in moss life histori es occurred at the level of genus and that life histories have been re latively conserved in the process of subsequent cladogenesis. The pers istent occurrence of water relations effects at several taxonomic leve ls, and the relatively large proportion of variance in life history tr aits, independent of taxonomic affiliation. for which these effects ac count, may imply adaptive coevolution of water relations and life hist ory. These ideas can best be tested in an explicitly phylogenetic fram ework.