Historical biogeography of tamarins, genus Saguinus: the molecular phylogenetic evidence

Hypotheses of the historical biogeography of tamarins (genus Saguinus) based on variation in coat colors and body size are tested using phylogenetic relationships inferred from mitochondrial DNA (mtDNA) sequence data. Samples from all 12 species of Saguinus and several subspecies are included in the analysis. Approximately 1,200 bases of mtDNA sequence from the cytochrome b and D-loop regions are reported for the tamarins and several outgroup taxa. Parsimony analysis of the mtDNA sequence data reveals Saguinus to be a monophyletic taxon composed of two major clades: one, the Small-bodied clade, contains S. nigricollis, S. tripartitus, and S. fuscicollis, and the other, the Large-bodied clade, contains the other nine species. The phylogenetic relationships among tamarins inferred from the mtDNA sequence data reject previous hypotheses for the historical biogeography of tamarins and suggest different dispersal routes for this group of New World monkeys. The molecular data suggest that tamarins dispersed across South America in two major waves from an origin somewhere south of the Amazon. One wave moved in a westerly direction, whereas the other moved in a northeastern direction toward the Amazon delta and then west along the northern portion of the continent into northern Colombia and Panama.     

Origin of a fungal symbiont of perennial ryegrass by interspecific hybridization of a mutualist with the ryegrass choke pathogen, Epichlo? typhina

Seed-borne fungal symbionts (endophytes) provide many cool-season grass species with biological protection from biotic and abiotic stresses. The endophytes are asexual, whereas closely related sexual species of genus Epichlo? (Clavicipitales) cause grass choke disease. Perennial ryegrass (Lolium perenne) is a host of two endophyte taxa, LpTG-1 (L. perenne endophyte taxonomic grouping one = Acremonium lolii) and LpTG-2, as well as the choke pathogen, Epichlo? typhina (represented by isolate E8). Relationships among these fungi and other Epichlo? species were investigated by analysis of gene sequences, DNA polymorphisms and allozymes. The results indicate that LpTG-2 is a heteroploid derived from an interspecific hybrid. The LpTG-2 isolates had two copies each of nine out of ten genes analyzed (the exception being the rRNA gene locus), and the profiles for seven of these were composites of those from E. typhina E8 and A. lolii isolate Lp5. Molecular phylogenetic analysis grouped the two beta-tubulin genes of LpTG-2 into separate clades. One (tub2-1) was related to that of E. typhina E8, and the other (tub2-2) to that of A. lolii. The mitochondrial DNA profile of LpTG-2 was similar to that of A. lolii, but its rRNA gene sequence grouped it with E. typhina E8. A proposed model for the evolution of LpTG-2 involves infection of a L. perenne-A. lolii symbiotum by E. typhina, followed by hybridization of the two fungi. Such interspecific hybridization may be a common and important mechanism for genetic variation in Epichlo? endophytes.     

Function of proteoglycans in the extracellular matrix

Estimating phylogenies from DNA sequence data has become the major methodology of molecular phylogenetics. To date, molecular phylogenetics of the vertebrates has been very dependent on mtDNA, but studies involving mtDNA are limited because the several genes comprising the mt-genome are inherited as a single linkage group. The only apparent solution to this problem is to sequence additional genes, each representing a distinct linkage group, so that the resultant gene trees provide independent estimates of the species tree. There exists the need to find novel gene sequences which contain enough phylogenetic information to resolve relationships between closely related species. A possible source is the nuclear-encoded introns, because they evolve more rapidly than exons. We designed primers to amplify and sequence the 7 intron from the beta-fibrinogen gene for a recently evolved group, the woodpeckers. We sequenced the entire intron for 10 specimens representing five species. Nucleotide substitutions are randomly distributed along the length of the intron, suggesting selective neutrality. A preliminary analysis indicates that the phylogenetic signal in the intron is as strong as that in the mitochondrial encoded cytochrome b (cyt b) gene. The topology of the beta-fibrinogen tree is identical to that of the cyt b tree. This analysis demonstrates the ability of the 7 intron of beta-fibrinogen to provide well resolved, independent gene trees for recently evolved groups and establishes it as a source of sequences to be used in other phylogenetic studies.     

Species-specific segregation of gender-associated mitochondrial DNA types in an area where two mussel species (Mytilus edulis and M. trossulus) hybridize

In each of the mussel species Mytilus edulis and M. trossulus there exist two types of mtDNA, the F type transmitted through females and the M type transmitted through males. Because the two species produce fertile hybrids in nature, F and M types of one may introgress into the other. We present the results from a survey of a population in which extensive hybridization occurs between these two species. Among specimens classified as "pure" M. edulis or "pure" M. trossulus on the basis of allozyme analysis, we observed no animal that carried the F or the M mitotype of the other species. In most animals of mixed nuclear background, an individual's mtDNA came from the species that contributed the majority of the individual's nuclear genes. Most importantly, the two mtDNA types in post-F1 male hybrids were of the same species origin. We interpret this to mean that there are intrinsic barriers to the exchange of mtDNA between these two species. Because such barriers were not noted in other hybridizing species pairs (many being even less interfertile than M. edulis and M. trossulus), their presence in Mytilus could be another feature of the unusual mtDNA system in this genus.     

Phylogenetic evidence for role-reversals of gender-associated mitochondrial DNA in Mytilus (Bivalvia: Mytilidae)

Distinct gender-associated mitochondrial DNA (mtDNA) lineages (i.e., lineages which are transmitted either through males or through females) have been demonstrated in two families of bivalves, the Mytilidae (marine mussels) and the Unionidae (freshwater mussels), which have been separated for more than 400 Myr. The mode of transmission of these M (for male-transmitted) and F (for female-transmitted) molecules has been referred to as doubly uniparental inheritance (DUI), in contrast to standard maternal inheritance (SMI), which is the norm in animals. A previous study suggested that at least three origins of DUI are required to explain the phylogenetic pattern of M and F lineages in freshwater and marine mussels. Here we present phylogenetic evidence based on partial sequences of the cytochrome c oxidase subunit I gene and the 16S RNA gene that indicates the DUI is a dynamic phenomenon. Specifically, we demonstrate that F lineages in three species of Mytilus mussels, M. edulis, M. trossulus, and M. californianus, have spawned separate lineages which are now associated only with males. This process is referred to as "masculinization" of F mtDNA. By extension, we propose that DUI may be a primitive bivalve character and that periodic masculinization events combined with extinction of previously existing M types effectively reset the time of divergence between conspecific gender-associated mtDNA lineages.     

Clustering of Caucasian Leber hereditary optic neuropathy patients containing the 11778 or 14484 mutations on an mtDNA lineage

Leber hereditary optic neuropathy (LHON) is a type of blindness caused by mtDNA mutations. Three LHON mtDNA mutations at nucleotide positions 3460, 11778, and 14484 are specific for LHON and account for 90% of worldwide cases and are thus designated as "primary" LHON mutations. Fifteen other "secondary" LHON mtDNA mutations have been identified, but their pathogenicity is unclear. mtDNA haplotype and phylogenetic analysis of the primary LHON mutations in North American Caucasian patients and controls has shown that, unlike the 3460 and 11778 mutations, which are distributed throughout the European-derived (Caucasian) mtDNA phylogeny, patients containing the 14484 mutation tended to be associated with European mtDNA haplotype J. To investigate this apparent clustering, we performed chi2-based statistical analyses to compare the distribution of LHON patients on the Caucasian phylogenetic tree. Our results indicate that, unlike the 3460 and 11778 mutations, the 14484 mutation was not distributed on the phylogeny in proportion to the frequencies of the major Caucasian mtDNA haplogroups found in North America. The 14484 mutation was next shown to occur on the haplogroup J background more frequently that expected, consistent with the observation that approximately 75% of worldwide 14484-positive LHON patients occur in association with haplogroup J. The 11778 mutation also exhibited a moderate clustering on haplogroup J. These observations were supported by statistical analysis using all available mutation frequencies reported in the literature. This paper thus illustrates the potential importance of genetic background in certain mtDNA-based diseases, speculates on a pathogenic role for a subset of LHON secondary mutations and their interaction with primary mutations, and provides support for a polygenic model for LHON expression in some cases.     

A comparative study of vertebrate eye lens crystallins using isoelectric focusing and densitometry

1. The crystallin proteins of numerous species belonging to different classes of vertebrates have been studied. 2. Species-specific crystallin patterns are revealed which unequivocally characterize the different species. 3. A marked variability in the number and percentage of alpha-, beta- and gamma-crystallins were found in the various species. 4. The gamma-crystallin family, with a meagre number of common bands, has proved to be most representative of the species. The beta-crystallins, with their greater number of common bands, have been best preserved throughout vertebrate evolution. 5. From the similarity coefficient matrix a dendrogram is drawn up, a visual phylogenetic summary of the interrelationships between the vertebrates considered. 6. In the Discussion, other aspects are considered, such as lens morphology, functionality, animal age, post-synthetic modifications and genetic factors.     

Plasmon analyses of Triticum (wheat) and Aegilops: PCR-single-strand conformational polymorphism (PCR-SSCP) analyses of organellar DNAs

To investigate phylogenetic relationships among plasmons in Triticum and Aegilops, PCR-single-strand conformational polymorphism (PCR-SSCP) analyses were made of 14.0-kb chloroplast (ct) and 13. 7-kb mitochondrial (mt)DNA regions that were isolated from 46 alloplasmic wheat lines and one euplasmic line. These plasmons represent 31 species of the two genera. The ct and mtDNA regions included 10 and 9 structural genes, respectively. A total of 177 bands were detected, of which 40.6% were variable. The proportion of variable bands in ctDNA (51.1%) was higher than that of mtDNA (28. 9%). The phylogenetic trees of plasmons, derived by two different models, indicate a common picture of plasmon divergence in the two genera and suggest three major groups of plasmons (Einkorn, Triticum, and Aegilops). Because of uniparental plasmon transmission, the maternal parents of all but one polyploid species were identified. Only one Aegilops species, Ae. speltoides, was included in the Triticum group, suggesting that this species is the plasmon and B and G genome donor of all polyploid wheats. ctDNA variations were more intimately correlated with vegetative characters, whereas mtDNA variations were more closely correlated with reproductive characters. Plasmon divergence among the diploids of the two genera largely paralleled genome divergence. The relative times of origin of the polyploid species were inferred from genetic distances from their putative maternal parents.     

Multiregional introgressions inferred from the mitochondrial DNA phylogeny of a hybridizing species complex of gobiid fishes, genus Tridentiger

Partial sequences of the cytochrome b gene (402 bp) in mtDNA were determined for brackishwater gobiid fishes, genus Tridentiger, collected from geographically distant locations in the Japanese Archipelago, and their interspecific and geographic variations were analyzed and compared. Contrary to the results of a previous allozyme analysis which revealed the existence of considerable genetic divergence (Nei's genetic distance > 0.5) between T. obscurus and T. brevispinis, the mtDNA haplotypes (mitotypes) of these two species were very similar and could not be distinguished by any of the neighbor-joining, maximum-likelihood or parsimony analyses. Hybrid individuals between the two species were also found, with several mitotypes being shared by both species and their hybrids. The phylogenetic relationships of mitotypes were divided into three subgroups, the geographical distributions of the latter being allied to geographical features of the Archipelago. These results suggested the occurrence of multiregional introgression between the two species, with mitotypes transferring from one species to the other.     

Mitochondrial DNA polymorphism in Jindo dogs

Mitochondrial DNA (mtDNA) polymorphism was studied in 21 Jindo dogs inhabiting Jin Island off the Korean peninsula. The polymorphism was analyzed with 10 restriction endonucleases that recognize six base pairs. The sizes of the mtDNA fragments produced by digestion using each endonucleases were separated by agarose gel electrophoresis, and the polymorphisms were detected with Japanese mongrel dog mtDNA as a probe. The mtDNA polymorphism in Jindo dogs was observed with four restriction endonucleases, Apa I, EcoR V, Hinc II, and Sty I. However, no polymorphism was detected with BamH I, Bgl II, EcoR I, Hind III, Pst I, or Xba I. The observed restriction endonuclease morphs were classified into 4 types of distinct cleavage patterns. The average number of nucleotide substitutions per nucleotide site in Jindodogs was estimated to be 0.0086. By UPG phylogenetic analysis, the 4 mtDNA types showed only one cluster. This suggests that Jindo dogs have not diverged from the other cluster up to the present and the species is considerably pure.     

Comparison between the complete mtDNA sequences of the blue and the fin whale, two species that can hybridize in nature

The sequence of the mitochondrial DNA (mtDNA) molecule of the blue whale (Balaenoptera musculus) was determined. The molecule is 16,402 bp long and its organization conforms with that of other eutherian mammals. The molecule was compared with the mtDNA of the congeneric fin whale (B. physalus). It was recently documented that the two species can hybridize and that male offspring are infertile whereas female offspring may be fertile. The present comparison made it possible to determine the degree of mtDNA difference that occurs between two species that are not completely separated by hybridization incompatibility. The difference between the complete mtDNA sequences was 7.4%. Lengths of peptide coding genes were the same in both species. Except for a small portion of the control region, disruption in alignment was usually limited to insertion/deletion of a single nucleotide. Nucleotide differences between peptide coding genes ranged from 7.1 to 10.5%, and difference at the inferred amino acid level was 0.0-7.9%. In the rRNA genes the mean transition difference was 3.8%. This figure is similar in degree to the difference (3.4%) between the 12S rRNA gene of humans and the chimpanzee. The mtDNA differences between the two whale species, involving both peptide coding and rRNA genes, suggest an evolutionary separation of > or = 5 million years. Although hybridization between more distantly related mammalian species may not be excluded, it is probable that the blue and fin whales are nearly as different in their mtDNA sequences as hybridizing mammal species may be.     

Phylogenetic relationships among Agamid lizards of the Laudakia caucasia species group: testing hypotheses of biogeographic fragmentation and an area cladogram for the Iranian Plateau

Phylogenetic relationships within the Laudakia caucasia species group on the Iranian Plateau were investigated using 1708 aligned bases of mitochondrial DNA sequence from the genes encoding ND1 (subunit one of NADH dehydrogenase), tRNAGln, tRNAIle, tRNAMet, ND2, tRNATrp, tRNAAla, tRNAAsn, tRNACys, tRNATyr, and COI (subunit I of cytochrome c oxidase). The aligned sequences contain 207 phylogenetically informative characters. Three hypotheses for historical fragmentation of Laudakia populations on the Iranian Plateau were tested. In two hypotheses, fragmentation of populations is suggested to have proceeded along continuous mountain belts that surround the Iranian Plateau. In another hypothesis, fragmentation is suggested to have resulted from a north-south split caused by uplifting of the Zagros Mountains in the late Miocene or early Pliocene [5-10 MYBP (million years before present)]. The shortest tree suggest the later hypothesis, and statistical tests reject the other two hypothesis. The phylogenetic tree is exceptional in that every branch is well supported. Geologic history provides dates for most branches of the tree. A plot of DNA substitutions against dates from geologic history refines the date for the north-south split across the Iranian Plateau to 9 MYBP (late Miocene). The rate of evolution for this segment of mtDNA is 0.65% (0.61-0.70%) change per lineage per million years. A hypothesis of area relationships for the biota of the Iranian Plateau is generated from the phylogenetic tree.     

PDLLA microspheres containing steroids: spray-drying, o/w and w/o/w emulsifications as preparation methods

Sea urchins of the genus Arbacia (order Stirodonta) have discontinuous allopatric distributions ranging over thousands of kilometers. Mitochondrial DNA (mtDNA) sequences were used to reconstruct phylogenetic relationships of four Arbacia species and their geographic populations. There is little evidence of genetic structuring of populations within species, except in two cases at range extremes. The mtDNA sequence differentiation between species suggests that divergence occurred about 4-9 MYA. Gene sequences encoding the sperm protein bindin and its intron were obtained and compared with the mtDNA phylogeny. Sea urchins among the well-studied echinoid order Camarodonta, with degrees of mtDNA divergence similar to those of Arbacia species, are known to have remarkable variation in bindin. However, in Arbacia, little variation in deduced amino acid sequences of bindin was found, indicating that purifying selection acts on the protein. In contrast, bindin intron sequences showed much differentiation, including numerous insertion/deletions. Fertilization experiments performed between a divergent pair of Arbacia species from the Atlantic and Pacific Oceans revealed no evidence of blocks to gamete recognition. In Arbacia, fertilization specificities may have evolved relatively slowly as a result of extensive gene flow within species, greater functional constraint on the bindin polypeptide, or reduced selective pressure for species recognition in singly occurring species.     

A molecular perspective on the systematics and evolution of the genus Arvicanthis (Rodentia, Muridae): inferences from complete cytochrome b gene sequences

Systematics of the genus Arvicanthis, the African unstriped grass rat, are somewhat controversial. Most recent taxonomic revisions list five to six species but the definition of some of these (Arvicanthis dembeensis, Arvicanthis nairobae, and Arvicanthis niloticus) is uncertain. The complete mitochondrial cytochrome b gene (1140 bp) was sequenced for 20 specimens from throughout the range of the genus to determine the intrageneric genetic structure, construct a molecular phylogeny, and evaluate classical taxonomies. Neighbor-joining and maximum parsimony analyses yielded identical phylogenetic trees that identify two major lineages: the first one (1) is composed of specimens usually referred to A. niloticus but representing several distinct species, and the other (2) is a complex including "true" A. niloticus from Egypt and northern West Africa as well as Arvicanthis abyssinicus, Arvicanthis dembeensis, and Arvicanthis somalicus. An analysis on a 357-bp fragment of the cytochrome b including published data on A. nairobae indicates that this taxon is part of clade (1). Calibration of the number of 3rd position transversion changes with the murid fossil record suggests that clades (1) and (2) diverged approximately 5 Myr ago. Arvicanthis niloticus as currently recognized is a paraphyletic association and this name should be restricted to the Egyptian and northern West African sample. We also suggest referring to A. dembeensis as A. niloticus, as our cytochrome b data do not support its recognition as a distinct species. Clade (1) is subdivided in three lineages, geographically corresponding to southern West, Central, and East Africa. The high genetic divergence detected between the Central African lineage and the other two lineages suggests that they probably represent separate species. Clade (2) experienced rapid cladogenetic events during the late Pliocene, with the A. somalicus lineage being the first to emerge, followed by the ancestor of A. abyssinicus and A. blicki. This period was characterized by significant climatic and environmental changes, such as the extension of open habitats, which might have provided a stimulus for speciation in this savanna-dwelling genus. Confrontation of our molecular results with chromosomal data shows a high degree of congruence between the two datasets.     

Phylogenetics and the origin of species

A recent criticism that the biological species concept (BSC) unduly neglects phylogeny is examined under a novel modification of coalescent theory that considers multiple, sex-defined genealogical pathways through sexual organismal pedigrees. A competing phylogenetic species concept (PSC) also is evaluated from this vantage. Two analytical approaches are employed to capture the composite phylogenetic information contained within the braided assemblages of hereditary pathways of a pedigree: (i) consensus phylogenetic trees across allelic transmission routes and (ii) composite phenograms from quantitative values of organismal coancestry. Outcomes from both approaches demonstrate that the supposed sharp distinction between biological and phylogenetic species concepts is illusory. Historical descent and reproductive ties are related aspects of phylogeny and jointly illuminate biotic discontinuity.     

Gene rearrangements in snake mitochondrial genomes: highly concerted evolution of control-region-like sequences duplicated and inserted into a tRNA gene cluster

Mitochondrial DNA (mtDNA) regions corresponding to two major tRNA gene clusters were amplified and sequenced for the Japanese pit viper, himehabu. In one of these clusters, which in most vertebrates characterized to date contains three tightly connected genes for tRNA(Ile), and tRNA(Gln), and tRNA(Met), a sequence of approximately 1.3 kb was found to be inserted between the genes for tRNA(Ile) and tRNA(Gln). The insert consists of a control-region-like sequence possessing some conserved sequence blocks, and short flanking sequences which may be folded into tRNA(Pro), tRNA(Phe), and tRNA(Leu) genes. Several other snakes belonging to different families were also found to possess a control-region-like sequence and tRNA(Leu) gene between the tRNA(Ile)and tRNA(Gln) genes. We also sequenced a region surrounded by genes for cytochrome b and 12S rRNA, where the control region and genes for tRNA(Pro) and tRNA(Phe) are normally located in the mtDNAs of most vertebrates. In this region of three examined snakes, a control-region-like sequence exists that is almost completely identical to the one found between the tRNA(Ile) and tRNA(Gln) genes. The mtDNAs of these snakes thus possess two nearly identical control-region-like sequences which are otherwise divergent to a large extent between the species. These results suggest that the duplicate state of the control-region-like sequences has long persisted in snake mtDNAs, possibly since the original insertion of the control-region-like sequence and tRNA(Leu) gene into the tRNA gene cluster, which occurred in the early stage of the divergence of snakes. It is also suggested that the duplicated control-region-like sequences at two distant locations of mtDNA have evolved concertedly by a mechanism such as frequent gene conversion. The secondary structures of the determined tRNA genes point to the operation of simplification pressure on the T psi C arm of snake mitochondrial tRNAs.     

Diversity and age of the four major mtDNA haplogroups, and their implications for the peopling of the New World

Despite considerable investigation, two main questions on the origin of Native Americans remain the topic of intense debate-namely, the number and time of the migration(s) into the Americas. Using the 720 available Amerindian mtDNA control-region sequences, we reanalyzed the nucleotide diversity found within each of the four major mtDNA haplogroups (A-D) thought to have been present in the colonization of the New World. We first verified whether the within-haplogroup sequence diversity could be used as a measure of the haplogroup's age. The pattern of shared polymorphism, the mismatch distribution, the phylogenetic trees, the value of Tajima's D, and the computer simulations all suggested that the four haplogroups underwent a bottleneck followed by a large population expansion. The four haplogroup diversities were very similar to each other, offering a strong support for their single origin. They suggested that the beginning of the Native Americans' ancestral-population differentiation occurred approximately 30,000-40,000 years before the present (ybp), with a 95%-confidence-interval lower bound of approximately 25,000 ybp. These values are in good agreement with the New World-settlement model that we have presented elsewhere, extending the results initially found for haplogroup A to the three other major groups of mtDNA sequences found in the Americas. These results put the peopling of the Americas clearly in an early, pre-Clovis time frame.     

Wolbachia in two insect host-parasitoid communities

Wolbachia form a group of intracellular bacteria that alter reproduction in their arthropod hosts. Two major phylogenetic subdivisions (A and B) of Wolbachia occur. Using a polymerase chain reaction assay we surveyed for the A and B group Wolbachia in 82 insect species from two temperate host-parasitoid communities (food webs) and a general collection of Lepidoptera caught at a light trap. One host-parasitoid community was based around leaf-mining Lepidoptera, and the other around Aphids. We found that: (i) 22.0% of insects sampled were infected with Wolbachia; and (ii) the prevalence and type (A or B) of Wolbachia infection differed significantly between communities and taxonomic groups. We obtained DNA sequences from the ftsZ gene for the group B Wolbachia found in six leaf-mining species and one of their parasitoids, as well as four of the Lepidoptera caught by a light trap. Taken together, the results of our survey and phylogenetic analyses of the sequence data suggest that host-parasitoid transfer of Wolbanchia is not the major route through which the species we have examined become infected. In addition, the Wolbachia strains observed in five leaf-mining species from the same genus were not closely related, indicating that transfer between species has not occurred due to a shared feeding niche or cospeciation.     

Heteroplasmy, length and sequence variation in the mtDNA control regions of three percid fish species (Perca fluviatilis, Acerina cernua, Stizostedion lucioperca)

The nucleotide sequence of the control region and flanking tRNA genes of perch (Perca fluviatilis) mtDNA was determined. The organization of this region is similar to that of other vertebrates. A tandem array of 10-bp repeats, associated with length variation and heteroplasmy was observed in the 5' end. While the location of the array corresponds to that reported in other species, the length of the repeated unit is shorter than previously observed for tandem repeats in this region. The repeated sequence was highly similar to the Mt5 element which has been shown to specifically bind a putative D-loop DNA termination protein. Of 149 perch analyzed, 74% showed length variation heteroplasmy. Single-cell PCR on oocytes suggested that the high level of heteroplasmy is passively maintained by maternal transmission. The array was also observed in the two other percid species, ruffe (Acerina cernua) and zander (Stizostedion lucioperca). The array and the associated length variation heteroplasmy are therefore likely to be general features of percid mtDNAs. Among the perch repeats, the mutation pattern is consistent with unidirectional slippage, and statistical analyses supported the notion that the various haplotypes are associated with different levels of heteroplasmy. The variation in array length among and within species is ascribed to differences in predicted stability of secondary structures made between repeat units.     

Cultural selection and genetic diversity in matrilineal whales

Low diversities of mitochondrial DNA (mtDNA) have recently been found in four species of matrilineal whale. No satisfactory explanation for this apparent anomaly has been previously suggested. Culture seems to be an important part of the lives of matrilineal whales. The selection of matrilineally transmitted cultural traits, upon which neutral mtDNA alleles "hitchhike," has the potential to strongly reduce genetic variation. Thus, in contrast to other nonhuman mammals, culture may be an important evolutionary force for the matrilineal whales.