A comparative phenetic and cladistic analysis of the genus Holcaspis Chaudoir (Coleoptera: Carabidae)

Abstract

The systematics of the endemic New Zealand carabid genus Holcaspis are investigated, using phenetic and cladistic methods, to construct phenetic and phylogenetic relationships. Three different character data sets: morphological, allozyme and random amplified polymorphic DNA (RAPD) based on the polymerase chain reaction (PCR), are used to estimate the relationships.

Cladistic and morphometric analyses are undertaken on adult morphological characters. Twenty six external morphological characters, including male and female genitalia, are used for cladistic analysis. The results from the cladistic analysis are strongly congruent with previous publications.

The morphometric analysis uses multivariate discriminant functions, with 18 morphometric variables, to derive a phenogram by clustering from Mahalanobis distances (D²) of the discrimination analysis using the unweighted pair-group method with arithmetical averages (UPGMA). In contrast to the cladistic analysis, the phonetic clustering results in a less useful estimation of affinities of the genus. However, this analysis reveals a method with a relatively high probability of assigning an individual to the correct species (70%-100%). Therefore morphometric analysis is shown to be useful for species identification.

Allozyme data are derived by electrophoresis using a cellulose acetate medium. A total of 42 alleles of 13 presumptive loci from 10 enzyme systems are used for cladistic and phenetic analysis of 13 Holcaspis species. A phenogram is generated by UPGMA clustering using a genetic distance matrix. Cladograms are constructed using both independent alleles and loci as characters. The cladograms from both allele and locus data are highly congruent with the phenogram derived from the genetic similarity matrix data. Intraspecific allozyme variation is also investigated with a limited number of populations and a relatively confined range of sample sites. A high degree of heterozygosity is revealed in H. oedicnema. The mean genetic similarity among the Holcaspis species is I= 0.382±0.142 and the mean genetic distance is D= l.055±0.143.

Molecular data are used in the intraspecific variation study and to estmate species relationships of Holcaspis. Optimal RAPD-PCR conditions such as primer concentration, magnesium chloride concentration and RAPD-PCR programme, are established for reproducible and informative amplifying of banding patterns of Holcaspis species. A total of 271 band positions are scored for all individuals studied and are subjected to both cladistic and phenetic analysis to estimate the species relationships. Phenograms using UPGMA are generated from both simple matching similarity coefficients and Jaccard's similarity coefficients. The resulting two phenograms are identical. Principal coordinate analysis is also used to demonstrate the relationships among species. The results are congruent with the phenograms. However, the pattern of species relationships is indistinct.

The cladogram generated from cladistic analysis shows relatively high congruence with the phenogram. In addition, the results from RAPD-PCR are much more congruent with the results from allozyme data than with the morphological data. The RAPD-PCR technique is, therefore, promising as a new tool for estimating phylogenetic relationships. In addition, the results show that the RAPD-PCR technique is a constructive, quick method for species grouping. From both RAPD-PCR and allozyme data, H. oedicnema shows extreme intraspecific variation that suggests that H. oedicnema is a species complex. To assess the best fit of phylogenetic relationships of the Holcaspis species, three character data sets: morphological, allozyme, and RAPD-PCR, are tested for congruence using both character congruence and taxonomic congruence method. The result indicates that the character congruence method of all character data sets combined produced a more informative result than the taxonomic congruence method. This study confirms the previous indication that H. punctigera and H. mordax are closely related both morphologically and genetically. The study suggests that H. ovatella is most genetically distinct from the rest of the Holcaspis species and that H. oedicnema is a genetically diverse species.