Message - 7th IAL Symposium

2A-1-P
Lichen: from genome to ecosystem in a changing world
(2A-1-P3) Submission ID: IAL0103-00001
PREDICTING SPECIES RICHNESS IN TROPICAL GRAPHIDACEAE BASED
ON PATTERNS OF EVOLUTION AND CHARACTER CORRELATION
Lücking R. 1 , Rivas Plata E. 2
1 Department of Botany, The Field Museum, Chicago, Illinois, United States
2 Department of Biology, Duke University, Durham, North Carolina, United States
A numerical approach is presented to quantitatively predict the number of potentially undiscovered species
within genera of Graphidaceae. The method uses a character correlation index (CCI) based on observed
versus expected frequencies of pairwise character state combinations in known species of a group to estimate
the degree of positive and negative evolutionary constraints in the co-occurrence of character states. These
are then used to detect ‘gaps’ in the taxonomic record, i.e. character combinations that have not been detected
in known species but are likely to occur in undiscovered ones. The method can be applied to organisms that
display a modular combination of characters, that is, they are comparatively poor in characters and species are
delimited by more or less free combinations of character states. This phenomenon is particularly common in
Fungi, including lichenized taxa, and is here used to predict species richness in the lichen genera Chroodiscus,
Clandestinotrema, Graphis, and Stegobolus, representing four distinct clades within the family. As one example,
the Graphis scripta group was studied. A total of 42 species is known in this group and, out of a total of 240 possible
character state combinations, a further 48 were found likely to represent undiscovered species, suggesting
that the real species number in this group is close to 90 or about twice the number currently known. This agrees
well with previous estimates for undiscovered diversity of tropical lichen species. The proposed method gives a
taxonomic prediction of how such ‘missing’ species might look like.
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