GOFFINET, BERNARD* AND A. JONATHAN SHAW. Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs CT, 06269 and Department of Botany, Duke University, Durham NC, 27708. - Dung and carcasses, the ultimate habitat within the dung-moss family (Splachnaceae)? Answers from a phylogenetic study based on cp DNA sequence data.
Seventy species distributed among 7 genera currently compose the
family Splachnaceae. Although many species are restricted to dung or
other animal remains for a substrate, others are terricolous or
epiphytic. Coprophilous species exhibit a series of
"adaptations" to their unique habitat: they produce
chemicals that attract insects that look for dung to lay their eggs;
the sterile tissue below the sporangium is expanded allowing for
insects to land on the sporophyte; they produce small sticky spores;
their capsule wall contracts upon drying and the spores are
continupously pushed up to the mouth of the sporangium by a
psuedocolumellea subtending the spore mass. Entomochorous taxa (i.e.,
those that use insects to disperse their spores) have traditionally
been considered derived within the family, with Splachnum
representing the ultimate product of this evolutionary trend. Here we
present phylogenetic analyses of sequences of two chloroplast loci
(trnL-trnF and rps4) for about 100 accessions, including exemplars of
all genera considered closely related to the Splachnaceae. Maximum
parsimony and likelihood analyses yield topologies wherein
Splachnum is resolved sister to a clade comprising all
remaining taxa. Within the latter, Tetraplodon whose species
are all thought to be entomophilous too, is sister to the
Taylorioideae. Brachymitrion, the sole genus lacking any
feature associated with entomophily, and occurring primarily in
epiphytic habitst, composes the most derived lineage. Most noticeable
is the recurrent association of anemophilous (using wind for spore
dispersal) and entomophilous species. Based on these results it is
hypothesized that entomophily was acquired early in the evolutionary
history of the Splachnaceae and subsequently lost multiple times.
This scenario would suggest that although highly specialized taxa may
be evolutionary dead ends, that they offer a source for subsequent
evolution of less specialized taxa, and thus may play in a significant
part in the diversification of these lineages.
Key words: Bryophytes, dung-mosses, entomochory, evolution, phylogeny, Splachnaceae