Phenotypic characters and ecology

a) Criteria for elaboration of the identification key

In order to assess the biodiversity of specific sites, habitats, or of an entire region as well, the investigator has to be able to at least separate the numerous collected specimens of the studied organisms in different categories and eventually different species. For this purpose, one of the most important tools is the identification keys and descriptions of taxa from previous works undertaken in similar habitats. Once the spectrum of the organismic diversity of that particular area, region or country is assessed the catalogation and elaboration of an identification key for the species reported locally is crucial for the development of further studies concerning the same organisms from that area.

When talking about microlichens and microfoliose lichens from north-eastern Brazil (CÁCERES 2007), an artificial group of lichenized fungi only distinguished by the growth form, the most important characters for the separation of the orders, families and genera are the most conspicuous ones, which concern to the reproductive structures, such as: presence or absence of fruit bodies, type of fruit bodies (if perithecioid or apothecioid), presence, absence and type of aphotecial margin, etc., to name a few.

Traditionally, the combination of phenotypical characthers is responsible for the identification of the lichen species, and for some groups and genera of lichenized fungi there are always some more relevant charachters than others. For example, after a recent study of the Graphidaceae by STAIGER (2002) it is considered that the presence or not of carbonization in the ascomata, if totally or partially carbonized, will distinguish already some new genera within that family. For the genus Cresponea, for instance, the separation of infra-generic taxa will be done by ascospores size and septation, as well as by the size of the apothecia. Also the secondary chemistry of medullary and cortical substances is essencial for the separation of species on some genera such as Herpothalon and Cryptothecia (CÁCERES et al. 2007c).

b) Distribution of diagnostic characters in each vegetation zone

As one of the results of the comparison between the lichen compositions of the three vegetation types, it was observed that some taxa can be considered as indicative of that particular habitat, according to the frequency data (CÁCERES et al. 2007b). There was then particular interest to note whether the proportions of the systematic units among these taxa

were of significat statiscal value.

Among the lichen species unique to the Zona da Mata, there is a higher proportion of the subclasses Arthoniomycetidae (Arthoniales: Arthoniaceae, Roccellaceae) and Chaeto-thyriomycetidae (Pyrenulales: Pyrenulaceae), as well as of the families Porinaceae and Thelotremataceae (Table 5), compared to the overall proportions of these taxa among all lichen species. Because of the aforementioned explanation, this difference is not significant, however (Chi-Square test). The Brejos de Altitude have a significantly higher proportion of Dothideomycetiae (Trypetheliaceae) and Ostropomycetidae (Ostropales: Gomphillaceae and Graphidadeae), as well as Pilocarpaceae (p < 0.05). Lecanoromycetidae (Lecanorales:

Lecanoraceae; Teloschistales: Physciaceae), as well as Pertusariales (Pertusariaceae) are the predominant subclasses, orders, and families found within the Caatinga sites (p < 0.001).

The predominant thallus type is squamulose for the Zona da Mata, byssoid for the Brejos de Altitude, and microfoliose for the Caatinga, but the observed differences are significant for the latter only (Table 5). Lichens in the Zona da Mata frequently have trentepohlioid photobionts (p < 0.05), while those in the Caatinga are associated with chlorococcoid photobionts (p < 0.001). Vegetative dispersal by isidia is more common within the Zona da Mata, while Caatinga lichens more frequently disperse by soredia, but the difference is not significant at the 5% level (Table 5). The predominant ascoma types are perithecia for the Zona da Mata, lirellae for the Brejos de Altitude, and apothecia and stromata for the Caatinga, but the patterns are not significant either. Ascospores are predominantly transversely septate and/or narrow in lichens of the Zona da Mata (not significant), thick-walled or muriform (p < 0.05) and hyaline in those of the Brejos de Altitude, and megalosporous, non-septate and/or brown (all p < 0.05) in Caatinga species.

Both Zona da Mata and Brejos de Altitude have no predominant secondary substances, except for psoromic acid in the first, but Caatinga lichens show a highly significant predominance of atranorin, lichexanthone and other xanthones, as well as pulvinic acid derivates, as cortical substances, and norstictic acid as medullary substance.

Table 5. Differences in the relative proportion of lichen species belonging to different higher taxa and showing different morphological, anatomical, and chemical features, between the three main vegetation types (Chi-Square test). Predominant taxa and features are indicated in bold face. ΤΤΤ = highly significant (p < 0.001), Τ = significant (p < 0.05), (Τ) = tendential (p

< 0.1), and (–) = not significant.

Zona da Mata p-level Brejos de Photobiont trentepohlioid Τ [none] (–) chlorococcoid ΤΤΤ

Ascoma type perithecia (–) lirellae (–) apothecia

Ascospore type [none] (–) thick-walled (–) megalosporou s

c) Scores – inconspicuous x conspicuous, abundant x rare, etc.

Apart from the appropriate tools for identifying the studied organisms, an efficient sampling method is extremely important in order to accurately estimate the organismical diversity in any given area. NEWMASTER et al. (2003) proposed for example a combination of already well-used methods for a better estimatition of the diversity of bryophites, when dealing with a variation of microhabitats. Similar works have been published as well regarding to lichen species richness estimatives, but on basis only of raw observation and own field experience of the collector.CÁCERES et. al (2007c) analysed the results of various field trips and inventories on 22 localities in northeastern Brazil, by applying three distinct sampling methods for corticolous microlichens.

After the completion of the major inventory of corticolous microlichens in the states of Rio Grande do Norte, Paraíba, Pernambuco, Alagoas and Sergipe (CÁCERES 2007), it was demonstrated that the chosen sampling technique was crucial for the estimation of the lichen specien richness of that area (CÁCERES et. al 2007c). On a raw scale, considering only localities with comparable ecological parameters, opportunistic sampling (method I) recovered only about one third the number of species on average than repetitive sampling (method II). On the other hand, quantitative sampling (method III) recovered more than five times the number of species than opportunistic sampling on average and 50% more species than repetitive sampling. This difference is explained by the idea that with the quantitative transect method, one is forced to collect specimens that one would usually not collect by means of visible inspection only, because they are either rare, inconspicuous, sterile, and/or cryptic, a notion that is confirmed by the significantly higher proportion of such species with the quantitative transect method, while the non-quantitative opportunistic method recovers a higher proportion of abundant, conspicuous, fertile, and/or distinctive taxa.

For each species, the four binary codes were added to a combined score CS, ranging from 0 (species rare, inconspicuous, sterile, and cryptic) to 4 (species abundant, conspicuous, fertile, and distinctive). Since the individual states for each parameter are independent of each other, any combination of codes is possible, for a total of 2⁴ = 16 combinations (Table 6).

Examples for combined score = 0 include all the sterile taxa (30 out of a total of 456) that were recognized as distinct species based on their morphology, anatomy, and chemistry, but could not be named due to the lack of critical systematic characters. Examples for combined score CS = 4 include Chapsa dilatata, Cryptothecia striata, Dichosporidium nigrocinctum,

Glyphis cicatricosa, Graphis chrysocarpa, Helminthocarpon leprevostii, Hemithecium chrysentheron, Lecanora caesiorubella, Lecanactis epileuca, Letrouitia domingensis, Malcolmiella badimioides, Maronina multifera, Ocellularia bahiana, Ochrolechia africana, Phaeographis haematites, Pyrenula mamillana, Sarcographa labyrinthica, and Trypethelium tropicum.

The most striking examples of cryptic species that were recovered by applying a combinations of sampling techniques are the genera Cryptothecia and Herpothallon, whose species are frequently sterile and form white or pale green crusts that are easily seen but which do not usually call the attention of the opportunistic collector since they appear to belong to the same species and are not very promising candidates for successful identification. A large number of specimens of these two genera were collected within the transect, and microscopical and chemical examination revealed that the number of cryptic species was unusually high: what appeared as two different taxa in the field turned out to represent no less than nine different species after careful study in the laboratory. Other examples include the genera Bacidina, Coenogonium, Cryptolechia, Enterographa, Fellhanera, Ramonia, and Stictis, which are unlikely to be collected by opportunistic sampling due to their small and inconspicuous thalli and fruit bodies. Species of Coenogonium, as well as Graphis and several pyrenocarpous genera (Anisomeridium), are known to contain a high number of cryptic species which cannot be identified in the field (HARRIS 1995, LÜCKING et al. 2007), and also in these genera, quantitative transect sampling is likely to turn out higher species numbers than opportunistic sampling.

Table 6. Calculation of combined score for selected lichen parameters.

Abundance Conspicuous- ness

Fertility Distinctive- ness

Combined score CS

Example

0 0 0 0 0 Malcolmiella polycampia

0 0 0 1 1 Ocellularia sp. (red soralia)

0 0 1 0 1 Bactrospora macrospora

0 1 0 0 1 Herpothallon sp.

1 0 0 0 1 Porina conspersa

0 0 1 1 2 Bacidina penicillata

0 1 0 1 2 Cryptothecia punctosorediata

1 0 0 1 2 [no species found]

0 1 1 0 2 Graphis striatula

1 0 1 0 2 Arthopyrenia chinchonae

1 1 0 0 2 Chryothrix xanthina

0 1 1 1 3 Haematomma leprarioides

1 0 1 1 3 Chapsa alborosella

1 1 0 1 3 Herpothallon rubrocinctum

1 1 1 0 3 Cresponea leprieurii

1 1 1 1 4 Laurera megasperma