Carlos Olavarría

Low worldwide genetic diversity in the killer whale (Orcinus orca): implications for demographic history.

A low level of genetic variation in mammalian populations where the census population size is relatively large has been attributed to various factors, such as a naturally small effective population size, historical bottlenecks and social behaviour. The killer whale (Orcinus orca) is an abundant, highly social species with reduced genetic variation. We find no consistent geographical pattern of global diversity and no mtDNA variation within some regional populations. The regional lack of variation is likely to be due to the strict matrilineal expansion of local populations. The worldwide pattern and paucity of diversity may indicate a historical bottleneck as an additional factor.

Global diversity and oceanic divergence of humpback whales (Megaptera novaeangliae)

Humpback whales (Megaptera novaeangliae) annually undertake the longest migrations between seasonal feeding and breeding grounds of any mammal. Despite this dispersal potential, discontinuous seasonal distributions and migratory patterns suggest that humpbacks form discrete regional populations within each ocean. To better understand the worldwide population history of humpbacks, and the interplay of this species with the oceanic environment through geological time, we assembled mitochondrial DNA control region sequences representing approximately 2700 individuals (465 bp, 219 haplotypes) and eight nuclear intronic sequences representing approximately 70 individuals (3700 bp, 140 alleles) from the North Pacific, North Atlantic and Southern Hemisphere. Bayesian divergence time reconstructions date the origin of humpback mtDNA lineages to the Pleistocene (880 ka, 95% posterior intervals 550–1320 ka) and estimate radiation of current Northern Hemisphere lineages between 50 and 200 ka, indicating colonization of the northern oceans prior to the Last Glacial Maximum. Coalescent analyses reveal restricted gene flow between ocean basins, with long-term migration rates (individual migrants per generation) of less than 3.3 for mtDNA and less than 2 for nuclear genomic DNA. Genetic evidence suggests that humpbacks in the North Pacific, North Atlantic and Southern Hemisphere are on independent evolutionary trajectories, supporting taxonomic revision of M. novaeangliae to three subspecies.

Lack of divergence in the mitochondrial cytochrome b gene between Macruronus species (Pisces: Merlucciidae) in the Southern Hemisphere

Abstract Two species of grenadier, the blue grenadier (or hoki) Macruronus novaezelandiae and the Patagonian grenadier M. magellanicus, have been recorded in the Southern Hemisphere with disjunct distributions along southern Australia‐New Zealand and southern Chile‐Argentina, respectively. The extent of genetic difference between these two putative species was examined using partial sequences (n = 44; 405 bp) of the mitochondrial DNA cytochrome b gene in a phylogenetic analysis and in an analysis of molecular variance (AMOVA). Our analysis showed a lack of genetic differentiation between species (FST = ‐0.02275, F ST = ‐0.00250) and among stocks. This absence of genetic differences is consistent with recent larval and adult morphology data suggesting that the two species should be synonymised. A comparable lack of genetic isolation has been observed in other closely related taxa (genera Merluccius and Micromesistius) with similar disjunct distributions across the Southern Hemisphere.

Microsatellite Markers Reveal Strong Genetic Structure in the Endemic Chilean Dolphin

Understanding genetic differentiation and speciation processes in marine species with high dispersal capabilities is challenging. The Chilean dolphin, Cephalorhynchus eutropia, is the only endemic cetacean of Chile and is found in two different coastal habitats: a northern habitat with exposed coastlines, bays and estuaries from Valparaíso (33°02′S) to Chiloé (42°00′S), and a southern habitat with highly fragmented inshore coastline, channels and fjords between Chiloé and Navarino Island (55°14′S). With the aim of evaluating the potential existence of conservation units for this species, we analyzed the genetic diversity and population structure of the Chilean dolphin along its entire range. We genotyped 21 dinucleotide microsatellites for 53 skin samples collected between 1998 and 2012 (swab: n = 8, biopsy: n = 38, entanglement n = 7). Bayesian clustering and spatial model analyses identified two genetically distinct populations corresponding to the northern and southern habitats. Genetic diversity levels were similar in the two populations (He: 0.42 v/s 0.45 for southern and northern populations, respectively), while effective size population was higher in the southern area (Ne: 101 v/s 39). Genetic differentiation between these two populations was high and significant (FST = 0.15 and RST = 0.19), indicating little or no current gene flow. Because of the absence of evident geographical barriers between the northern and southern populations, we propose that genetic differentiation may reflect ecological adaptation to the different habitat conditions and resource uses. Therefore, the two genetic populations of this endemic and Near Threatened species should be considered as different conservation units with independent management strategies.

Southernmost Distribution of Common Bottlenose Dolphins (Tursiops truncatus) in the Eastern South Pacific

The common bottlenose dolphin (Tursiops truncatus) is a cosmopolitan species that does not range to latitudes greater than 45o in either hemisphere, with a few exceptions. In South American waters, this species is generally distributed in the Atlantic Ocean south to Chubut province (ca. 46o S), while in the eastern South Pacific this species has been recorded in northern and central Chile, with a few records south to 40o S. Here we summarize recent records of common bottlenose dolphins obtained during systematic marine mammal surveys in the Chilean Patagonian and Fuegian channels and fjords (the Los Lagos, Aysén, and Magallanes regions of Chile). These data suggest an extension of the documented range of the species southwards, indicating that bottlenose dolphins may have colonized new areas in the eastern South Pacific or as the result of an increase in survey efforts by scientists in the region.

Occurrence and distribution of Chilean dolphin (Cephalorhynchus eutropia) in coastal waters of central Chile

Abstract The Chilean dolphin, Cephalorhynchus eutropia, is an endemic species distributed along the central‐southern coast of Chile. Biological and ecological knowledge about this species is insufficient; it is catalogued as Data Deficient “DD” by the World Conservation Union. This study provides information on the species’ occurrence and distribution along the central Chilean coast from January 2000 to March 2001. Monthly land‐based surveys were performed within the study area, which was divided by the Maule River outlet, with the northern area more influenced by an estuarine system than the southern one. Chilean dolphins were sighted in 83% of surveys. The relative abundance was significantly higher in the northern than the southern area (13.6 dolphins/h versus 3.5 dolphins/ h). Three behaviour categories were recorded (feeding, socialising, and travelling) in both areas, however, these were more frequently observed in the northern area. We suggest that the area located north of Maule River is the preferred zone for Chilean dolphins within the study area. This study shows a year‐round occurrence of Chilean dolphin in the study area which is possibly a critical habitat for this species. Further research focused on population structure assessment and residence patterns of the species in the study area is required.

Largest baleen whale mass mortality during strong El Niño event is likely related to harmful toxic algal bloom

While large mass mortality events (MMEs) are well known for toothed whales, they have been rare in baleen whales due to their less gregarious behavior. Although in most cases the cause of mortality has not been conclusively identified, some baleen whale mortality events have been linked to bio-oceanographic conditions, such as harmful algal blooms (HABs). In Southern Chile, HABs can be triggered by the ocean–atmosphere phenomenon El Niño. The frequency of the strongest El Niño events is increasing due to climate change. In March 2015, by far the largest reported mass mortality of baleen whales took place in a gulf in Southern Chile. Here, we show that the synchronous death of at least 343, primarily sei whales can be attributed to HABs during a building El Niño. Although considered an oceanic species, the sei whales died while feeding near to shore in previously unknown large aggregations. This provides evidence of new feeding grounds for the species. The combination of older and newer remains of whales in the same area indicate that MMEs have occurred more than once in recent years. Large HABs and reports of marine mammal MMEs along the Northeast Pacific coast may indicate similar processes in both hemispheres. Increasing MMEs through HABs may become a serious concern in the conservation of endangered whale species.

Ancient female philopatry, asymmetric male gene flow, and synchronous population expansion support the influence of climatic oscillations on the evolution of South American sea lion (Otaria flavescens)

The South American sea lion (Otaria flavescens) is widely distributed along the southern Atlantic and Pacific coasts of South America with a history of significant commercial exploitation. We aimed to evaluate the population genetic structure and the evolutionary history of South American sea lion along its distribution by analyses of mitochondrial DNA (mtDNA) and 10 nuclear microsatellites loci. We analyzed 147 sequences of mtDNA control region and genotyped 111 individuals of South American sea lion for 10 microsatellite loci, representing six populations (Peru, Northern Chile, Southern Chile, Uruguay (Brazil), Argentina and Falkland (Malvinas) Islands) and covering the entire distribution of the species. The mtDNA phylogeny shows that haplotypes from the two oceans comprise two very divergent clades as observed in previous studies, suggesting a long period (>1 million years) of low inter-oceanic female gene flow. Bayesian analysis of bi-parental genetic diversity supports significant (but less pronounced than mitochondrial) genetic structure between Pacific and Atlantic populations, although also suggested some inter-oceanic gene flow mediated by males. Higher male migration rates were found in the intra-oceanic population comparisons, supporting very high female philopatry in the species. Demographic analyses showed that populations from both oceans went through a large population expansion ~10,000 years ago, suggesting a very similar influence of historical environmental factors, such as the last glacial cycle, on both regions. Our results support the proposition that the Pacific and Atlantic populations of the South American sea lion should be considered distinct evolutionarily significant units, with at least two managements units in each ocean.

Stomach contents of long-finned pilot whales (Globicephala melas) from southern Chile

The widely distributed long-finned pilot whale (Globicephala melas) has been reported off the Chilean coast, from Iquique (20°12′S) south to Navarino Island (55°15′S; 67°30′W), but little is known about its biology or ecology in the region. Here, we report on the prey of this species, identified by stomach content analyses from animals stranded on Holget Islets, Beagle Channel, southern Chile in August 2006. The stomachs of seven individuals (six females and one male) contained cephalopod remains. The prey composition found in these southern Chilean pilot whales was similar to that described in other parts of the world and the Southern Ocean. This is the first report on the feeding habits of this species from Chile.

Occurrence of dwarf minke whales (Balaenoptera acutorostrata subsp.) around the Antarctic Peninsula

The occurrence of dwarf minke whales (Balaenoptera acutorostrata subsp.) around the Antarctic Peninsula was examined based on 406 sightings of minke whales recorded during the Chilean Antarctic Scientific Expeditions and other opportunistic cetacean surveys. Identification of the species was made only for the whales sighted in the proximity of the vessels when the specific diagnostic characters could be confirmed. Of the 406 sightings, 296 were assigned to Antarctic (519 individuals), nine (11 individuals) to dwarf and 101 to unidentified minke whales (149 individuals). Dwarf minke whales were identified by the reported external diagnostic characters for this species. Seven animals occurred around the South Shetland Island and four in the Gerlache Strait. In addition, another two animals were identified as dwarf minke whales in the Bellinghausen Sea in winter 1993, being these the most southern records for this species. These results confirm the occurrence of dwarf minke whales around the Antarctic Peninsula during the summer seasons, as well as in the Bellinghausen Sea in winter. The geographical range of these sightings was comprised between 61°03′ and 69°25′S and between 55°29′ and 86°53′W. These results also suggest that some dwarf minke whales remain in the Antarctic during the austral winter.