- Tissue samples for genetic analysis can be collected from museum specimens, carcasses, or live animals during rescue or tagging operations. DNA is extracted and sequenced from tissue samples and can answer a range of questions with important conservation implications.
- The study of genetics can inform conservation by providing an understanding of gene flow and movement between populations, helping to identify when populations are still in breeding contact, or whether populations are distinct or isolated from neighbouring populations, which can lend additional urgency to conservation efforts especially where populations size, health or diversity are found to be low.
- Sequencing of samples from products for sale in markets can help to identify when material (eg. oil or flesh) is from a river dolphin which can assist with enforcing the law and preventing trade in river dolphin products.
- Genetics is a vitally important tool for understanding the taxonomy of river dolphins and providing clarity regarding which species and populations are distinct, help with communication, fundraising and mobilising conservation efforts.
Why is understanding population structure and genetic health important for river dolphin conservation?
Although genetic studies may sound like they belong solely in the realm of laboratories and academic journals, they have very important conservation applications. While we know that almost all river dolphin populations are small and threatened, understanding more about a population’s potential genetic uniqueness, or separation from other neighbouring populations can lend additional urgency to efforts to protect that population. If genetic studies prove that a particular population can no longer be ‘replenished’ by interbreeding with neighbouring populations, or if a small population is found to have so little genetic diversity that it is at risk of in-breeding related health risks, it may be necessary to consider more aggressive conservation measures. On a more positive note, the granting of full species status to a population or subspecies can create a sense of pride for stakeholders, who feel a sense of ownership and investment in protecting ‘their’ species, and spur more effective conservation action.
How do we study dolphin population structure and genetic health?
The first step in genetic studies is the collection of tissue samples that can be sent to a lab for analysis. Only a tiny sliver of skin or other tissue (tooth, bone, blood or muscle) is required, and samples can be stored in ethanol, or a concentrated saline solution, at room temperature for several days after collection before freezing for long term storage. As such, it is relatively easy to collect samples from stranded or bycaught carcasses, or from live animals during rescue or satellite tagging operations. Samples can also be collected from bone or dried tissue in museums or other historical collections.
Once samples have been collected they can be analysed and used to address the following types of questions:
- Questions of taxonomy: Does a particular population, inhabiting a particular river basin represent a sub-population, a subspecies, or a species in its own right? There are clearly prescribed criteria for designating species and subspecies, which are continually being reviewed in light of new genetic techniques that are developed1, 2, and it can often take a long time to compile the necessary lines of evidence to make a strong case for species status. Genetic analysis, accompanied by detailed morphometric studies, has been used to support the recognition of the Ganges and Indus river dolphins as two separate species35. Deliberations are still underway to determine whether the Bolivian river dolphin, which is currently recognised as a sub-species of the Amazon river dolphin (Inia geoffrensis boliviensis), should be recognised as a full species. There is also a very strong case based on genetics, morphological differences and physical barriers to mixing to recognise the Araguaian river dolphin (putative species Inia araguaiaensis) as a separate species 616.
- Questions of population status or fragmentation: Genetics can also be used to demonstrate where and how populations are diverging into separate units that can no longer interbreed due to fragmentation of their habitat. This is the case in the Yangtze river, where genetic studies showed that barriers are preventing gene flow between the three remaining fragmented populations17, 18.
- Questions of genetic diversity and health: Species whose populations are already small may be reduced to such low levels that they are more susceptible to other problems associated with low population size, such as increased levels of inbreeding and the loss of genetic diversity through genetic drift. As a result, their risk of extinction may be substantially increased. This is a pervasive problem in river dolphins around the world where population sizes are decreasing. A study of Irrawaddy dolphins in the Mekong found that 85% of 60 sampled dolphins all shared the same maternally inherited haplotype, an indication of severe inbreeding depression, with the current population size only being 5% of its original/ancestral size19. The Indus river dolphin also suffers from very low genetic diversity3 as do the three remaining Yangtze finless porpoise populations17, 18.
- Other information that can be obtained from genetics: Advances in modern laboratory techniques now make it easier to generate longer genomic sequences that have increased the ability to understand things such as gene flow, past demographic events, historical population size, and the detection of genes under past or current selection. It is possible to use genetic fingerprinting to identify individuals thereby allowing for genetic capture-recapture methods to estimate population abundance, or identify movements of known finger-printed individuals, and genetics can also be used to identify the species of products for sale in markets or that are being traded illegally. Genetics is used for management by identifying ‘evolutionarily significant units’ that need to be managed separately from other components of a population.
- Taylor BL, Archer FI, Martien KK, et al. Guidelines and quantitative standards to improve consistency in cetacean subspecies and species delimitation relying on molecular genetic data. Marine Mammal Science 2017;33:132-55.
- Taylor BL, Perrin WF, Reeves RR, et al. Why we should develop guidelines and quantitative standards for using genetic data to delimit subspecies for data-poor organisms like cetaceans. Marine Mammal Science 2017;33:12-26.
- Braulik GT, Noureen U, Arshad M, Reeves RR. Review of status, threats, and conservation management options for the endangered Indus River blind dolphin. Biological Conservation 2015;192:30-41.
- Braulik GT, Barnett R, Odon V, Islas-Villanueva V, Hoelzel AR, Graves JA. One Species or Two? Vicariance, Lineage Divergence and Low mtDNA Diversity in Geographically Isolated Populations of South Asian River Dolphin. J Mammal Evol 2014:1-10.
- Braulik, G. T., F. Archer, U. Khan, M. Imran, R. K. Sinha, T. A. Jefferson, C. Donovan, and J. Graves. 2021. Taxonomic revision of the South Asian River dolphins (Platanista): Indus and Ganges River dolphins are separate species. Marine Mammal Science.
- Banguera-Hinestroza, E., H. Cardenas, M. Ruiz-Garcia, M. Marmontel, E. Gaitan, R. Vazquez & F. Garcia-Vallejo. 2002. Molecular identification of evolutionary significant units in the Amazon River dolphin Inia sp. (Cetacea: Iniidae). Journal of Heredity 93: 312-322
- da Silva, V., Trujillo, F., Martin, A., Zerbini, A.N., Crespo, E., Aliaga-Rossel, E. & Reeves, R. 2018. Inia geoffrensis. The IUCN Red List of Threatened Species 2018: e.T10831A50358152. https://dx.doi.org/10.2305/IUCN.UK.2018-2.RLTS.T10831A50358152.en. Downloaded on 25 February 2021
- Gravena, W., I.P. Faria, M.N. Da Silva, V. Da Silva & T. Hrbek. 2014a. Looking to the past and the future: were the Madeira river rapids a geographical barrier to the boto (Cetacea: Iniidae)? Conservation Genetics 15: 619-629.
- Gravena, W., I.P. Farias, M.N. Da Silva, V. Da Silva & T. Hrbek. 2014b. Madeira River Dams and the Boto: Possible Impacts on Population Structure. X Congreso de La Sociedad Latinoamericana de especialistas en Mamíferos Acuáticos. 16 Reunión de Expertos em Mamíferos Acuáticos de América Del Sur.
- Gravena, W., V. Da Silva, M.N. Da Silva, I.P. Farias & T. Hrbek. 2015. Living between rapids: genetic structure and hybridization in botos (Cetacea: Iniidade: Inia spp.) of the Madeira River, Brazil. Biological Journal of the Linnean Society 144: 764-777.
- Gravena, W., Fearnside, N. H., Tavares, É. S. G. M., Carvalho, N. D. M., Gross, M. C., Schneider, C. H., & da Silva, V. M. F. (2017). Caracterização citogenética do Boto da Bolívia (Inia boliviensis): mais uma ferramenta de diferenciação entre as espécies. Semina: Ciências Biológicas e da Saúde, 38(1supl), 115.
- IUCN. 2018. The IUCN Red List of Threatened Species. Version 2018-2. Available at: www.iucnredlist.org. (Accessed: 15 November 2018)
- Hrbek, T., V. da Silva, N. Dutra, W. Gravena, A.R. Martin & I.P. Farias. 2014. A new species of river dolphin from Brazil or: how little do we knows our biodiversity. PloS One9(1): e0083623. doi:10. 1371/journal.pone.0083623
- Ruiz-Garcıa, M., S. Caballero, M. Martinez-Aguero, & J.M. Shostell. 2008. Molecular differentiation among Inia geoffrensis and Inia boliviensis (Iniidae, Cetacea) by means of nuclear intron sequences. Pp. 177-203. In: Koven, V.T. (ed.), Population Genetics Research Progress,. Nova Publishers Inc., Boca Raton, FL, USA
- Siciliano, S., V.H. Valiati, R. Emin-Lima, A.F. Costa, J. Sartor, T. Dorneles, J. De Sousa e Silvia Jr. & L. Rosa de Oliveira. 2016b. New genetic data extend the range of river dolphins Inia in the Amazon delta. Hydrobiologia 777(1): 255-269.
- Tavera, G., E. Aliaga-Rossel, P. van Damme, & A. Crespo. 2010. Distribution and conservation status of the Bolivian river dolphin Inia boliviensis (d’Orbigny 1832). Pp. 99-122. In: Trujillo, F., E. Crespo, P. van Damme, & J.S. Usma. (eds.). Action Plan South American River Dolphins 2010-2020. WWF, Fundacion Omacha, WDS, WDCS, Solamac, Bogotá, D.C., Colombia.
- Xia, J., Zheng J, and Wang D., 2005. Ex situ conservation status of an endangered Yangtze finless porpoise population (Neophocaena phocaenoides asiaeorientalis) as measured from microsatellites and mtDNA diversity ICES Journal of Marine Science, 62: 1711-1716
- Chen M., Fontane M. C., Chehida Y. B., Zhang J., Labbe F., Mei Z., Hao Y., Wang K., Wu M., Zhao Q., & Wang D. 2017 Genetic footprint of population fragmentation and contemporary collapse in a freshwater cetacean. Scientific Report 7: 14449 DOI:10.1038/s41598-017-14812-z
- Krützen M, Beasley I, Ackermann CY, et al. Demographic collapse and low genetic diversity of the Irrawaddy dolphin population inhabiting the Mekong River. PLOS ONE 2018;13:e0189200.
- Taylor BL, Abel G, Miller P, et al. Ex situ options for cetacean conservation: December 2018 workshop, Nuremberg, Germany. Gland, Switzerland: IUCN; 2020.