Origins of the house crow
HOUSE crows or Corvus splendens are believed to pose health risks in the forms of pathogens such as Salmonella and E. coli ( Escherichia coli).
House crows may not migrate but that does not mean they have never travelled to another country or occasionally hitch-hiked by ship.
A recent study by Urszula Krzeminska, PhD (Doctor of Philosophy) candidate at Monash University Malaysia’s School of Science, with supervisors Dr Robyn Wilson, Dr Song Beng Kah, Prof Chris Austin and Prof Sadequr Rahman supported the possibility that Malaysian and Singaporean house crows may have travelled to Sri Lanka, Bangladesh and beyond.
The study, published in the journal Biological Invasions in April last year, is of interest to researchers of invasive species. Invasive species, also known as non-native or alien species, are introduced by humans to a new region deliberately or by accident.
They tend to multiply so much that they cause damage to human life or the environment. Their native homes are found mainly in South Asia, including Sri Lanka, Nepal, India and Bangladesh.
They have spread beyond those native regions to more than 20 countries. Although considered a tropical species, they can now be found even in the Netherlands.
The study looked at DNA (deoxyribonucleic acid) samples of house crows from Malaysia and Singapore as well as smaller samples from Kenya and South Africa to investigate their origins and genetic diversity.
DNA samples were collected from the crows’ liver tissue, feathers and blood. The Malaysian samples came from two densely populated states, Selangor and Penang. While most studies on invasive species use only one of two methods – either nuclear microsatellite markers or mitochondrial DNA markers – this study combined both.
The study by Krzeminska is the first to combine both methods in examining genetic diversity in samples of native and introduced house crows.
Another aim of the study was to determine the origins of current crow populations in Malaysia and Singapore.
The results affirm that house crows in Selangor may have been introduced from Sri Lanka or places near Sri Lanka more than 100 years ago.
There are records stating that 56 house crows were imported from Sri Lanka to Port Klang in the 1890s. These crows may have been imported to prevent caterpillar plagues and reduce human waste.
Meanwhile, the crows in Penang and Singapore most likely come from multiple sources outside of Malaysia.
More specifically, the crows of Singapore may have originated from Bangladesh or its neighbouring countries.
The study concluded that house crows could have spread from South Asia over the past 100 years by hitch-hiking on ships.
The house crows of Penang and Singapore had unexpectedly high levels of genetic diversity. While this finding could have been magnified by the small sample size, it also made sense as Penang and Singapore are busy port cities – and Singapore is the world’s second busiest port.
Meanwhile, the Selangor crow sample showed the least genetic diversity. This could be explained by the location of Selangor’s Port Klang.
The port lies in the middle of a long, narrow strait, which would have enabled ship-borne birds to make their landfall in many places along the west coast of the peninsula and diluted the diversity of crows that finally arrived in Klang.
This makes more sense if the Selangor crows originated from a single event in the 1890s when 56 birds were imported to Port Klang. If true, then Selangor crows demonstrate the founder effect, which occurs when a new colony is born from a rather small number of members. The result is reduced genetic diversity.
The study concluded that the house crow is an excellent model for studying genetic patterns and the evolution of populations in new environments.
These patterns could help researchers predict the degree of success and impact that an invasive species such as the Corvus splendus will have on a new environment.
For more information, visit www.sci.monash.edu.my.