Genetic and Morphological Approaches Distinguish the Three Sibling Species of theAnisakis simplexSpecies Complex, with a Species Designation asAnisakis berlandin. sp. forA. simplexsp. C (Nematoda: Anisakidae)

Abstract

Numerous specimens of the 3 sibling species of the Anisakis simplex species complex (A. pegreffii, A. simplex (senso stricto)), and A. simplex sp. C) recovered from cetacean species stranded within the known geographical ranges of these nematodes were studied morphologically and genetically. The genetic characterization was performed on diagnostic allozymes and sequences analysis of nuclear (internal transcribed spacer [ITS] of ribosomal [r]DNA) and mitochondrial (mitochondrial [mt]DNA cox2 and rrnS) genes. These markers showed (1) the occurrence of sympatry of the 2 sibling species A. pegreffii and A. simplex sp. C in the same individual host, the pilot whale, Globicephala melas Traill, from New Zealand waters; (2) the identification of specimens of A. pegreffii in the striped dolphin, Stenella coeruleoalba (Meyen), from the Mediterranean Sea; and (3) the presence of A. simplex (s.s.) in the pilot whale and the minke whale, Balaenoptera acutorostrata Lacépède, from the northeastern Atlantic waters. No F1 hybrids were detected among the 3 species using the nuclear markers. The phylogenetic inference, obtained by maximum parsimony (MP) analysis of separate nuclear (ITS rDNA region), combined mitochondrial (mtDNA cox2 and rrnS) sequences datasets, and by concatenated analysis obtained at both MP and Bayesian inference (BI) of the sequences datasets at the 3 studied genes, resulted in a similar topology. They were congruent in depicting the existence of the 3 species as distinct phylogenetic lineages, and the tree topologies support the finding that A. simplex (s.s.), A. pegreffii, and A. berlandi n. sp. (= A. simplex sp. C) represent a monophyletic group. The morphological and morphometric analyses revealed the presence of morphological features that differed among the 3 biological species. Morphological analysis using principal component analysis, and Procrustes analysis, combining morphological and genetic datasets, showed the specimens clustering into 3 well-defined groups. Nomenclatural designation and formal description are given for A. simplex species C: the name Anisakis berlandi n. sp. is proposed. Key morphological diagnostic traits are as follows between A. berlandi n. sp. and A. simplex (s.s.): ventriculus length, tail shape, tail length/total body length ratio, and left spicule length/total body length ratio; between A. berlandi n. sp. and A. pegreffii: ventriculus length and plectane 1 width/plectane 3 width ratio; and between A. simplex (s.s.) and A. pegreffii: ventriculus length, left and right spicule length/total body length ratios, and tail length/total body length ratio. Ecological data pertaining to the geographical ranges and host distribution of the 3 species are updated.

Anthropogenics: Human Influence on Global and Genetic Homogenization of Parasite Populations

“…obs. ;Santoro et al, 2014), whereas only low worm burdens were commonly found in Arctic boreal pinnipeds and fish (Mattiucci and Nascetti, 2007). A statistically significant correlation was observed between the abundance of the infection (A) as a measure of effective population size of parasite (N) and the value of genetic diversity (mean He) (Fig.…”

“…This was most apparent when examining distinct geographic areas such as in the Boreal and Austral hemispheres that are subject to diverse levels of habitat disturbance (Mattiucci and Nascetti, 2007). In this work, the genetic variability in anisakid populations from fish and marine mammals was examined with the use of 19 allozymes.…”

“…complex. Kendall's rank correlation, i.e., Kendall tau test, was performed to compare the abundance of infection (A) and the heterozygosity (He) in Contracaecum species sampled from Antarctic seals and fish hosts (gray circles), and from seals of the Arctic Boreal region (black circles) (data from Mattiucci and Nascetti, 2007). Parasite abundance was logtransformed, log(x þ 1).…”

“…If the determination of gene flow is based on the standardized variance of allele frequencies, Fst (Crow and Aoki, 1984;Slatkin and Barton, 1989), where m is the fraction of immigrant individuals in a population of effective size N, then among conspecific populations of anisakid nematodes, gene flow is generally found to be high. This is largely determined by the dispersal of host animals (Mattiucci et al, 1997) and parasite abundance (as a proxy for parasite population size); 2 parameters that are strongly correlated with host density (Arneberg et al, 1998). It follows, therefore, that variation in host dispersal and density would lead into differences in the patterns of genetic diversity distributed among anisakid parasite populations.…”

“…This has been attributed to the homogenetic effects of high gene flow, in association with the high dispersal capacity of the definitive cetacean hosts. Indeed, high levels of gene flow among populations, indirectly estimated from allele frequencies and Fst values have been observed (Mattiucci and Nascetti, 2008). Preliminary data from genetically monitoring anisakid populations over temporal scales indicate that the loss of polymorphism, i.e., ''genetic erosion,'' could have affected their gene pools.…”