Carrion crows, hooded crows, different or similar?


This 2017 video from the Czech republic is about hooded crows and carrion crows.

From the Ludwig-Maximilians-Universität München in Germany:

Speciation: Birds of a feather…

March 26, 2019

Carrion crows and hooded crows are almost indistinguishable genetically, and hybrid offspring are fertile. Ludwig-Maximilians-Universitaet (LMU) in Munich biologists now show that the two forms have remained distinct largely owing to the dominant role of plumage color in mate choice.

Crows have divided Europe between them. Western Europe is the realm of the soot-black carrion crow, while the eastern half of the continent is home to the hooded crow with its grayish black plumage. The boundary between the two populations — or more precisely, the hybrid zone where the two meet — is only 20-50 km wide, and in Germany it essentially follows the course of the River Elbe. This is the only stretch of territory in which both of these species are found and sucessfully mate with each other. The plumage of the fertile offspring of these pairings is intermediate in color between those of their parents. The sharp demarcation between the two populations, however, clearly indicates that gene flow across the hybrid zone is restricted, which implies that hybrids are at a selective disadvantage. “Defining speciation as the buildup of reproductive isolation, carrion crows and hooded crows are in the process of speciation”, says LMU evolutionary biologist Jochen Wolf. He and his research team have now analyzed the genetic basis for the division of European crows into two populations. Indeed, the results of the study demonstrate that the old saying “birds of a feather flock together” really does apply in this instance: The only genes that differ significantly between the two variants are those involved in determining the color of the plumage. This suggests that each form preferentially mates with partners of the same color as themselves. The new findings appear in the journal Nature Ecology and Evolution.

Europe’s crows once formed a single population. This is thought to have been broken up repeatedly during the last glacial maxima over the last tens to hundreds of thousand years ago, during which the crows retreated from Central Europe to milder refuges in Spain and the Balkans. At the end of the last Ice Age, they returned to their old haunts. But they had changed during the period of their isolation. “Most probably, a mutation had arisen in the easterly population, which endowed its carriers with a lighter colored, gray plumage”, says Wolf. Then carrion and hooded crows came into contact once again and formed a narrow hybrid zone. However, the genetic mechanisms responsible for maintaining the distinction between the two populations have remained unclear.

In order to identify these mechanisms, Wolf and his colleagues first sequenced the genomes of both carrion crows and hooded crows. “We found that the genomes of both forms are almost identical, and that the few genetic loci that differentiate gray from black crows are likely to be involved in determining the color of their plumage”, Wolf says. “We have now carried out a more detailed analysis and determined the degree of genetic mixing between the two populations. Using a technique known as admixture mapping we pinned down the genetic basis of their divergence.” To do so, his team examined the variant loci in the genomes of more than 400 birds — from within the hybrid zone and from the regions in which one or other of the two forms is endemic.

In this way, it was possible to identify the genes responsible for the difference in coloration between hooded and carrion crows. “The distinction can largely be explained by variation in just two genetic factors. In addition, we showed that these two loci interact with each other”, Wolf explains. In other words, these two factors together determine the color of the plumage. Further analyses confirmed that the rest of the genome can be freely exchanged between the two populations — and is common to carrion crows in Western Europe and the hooded crows in the eastern half of the continent. “Only two major effect genes which together encode the feather color differ sharply on either side of the hybrid zone — the gray alleles are not found to the west of the zone and the black allele is absent in the eastern region,” says Wolf. “That’s a very strong indication that there is rigorous selection on the basis of color.”

According to the authors of the study, these findings convincingly show that the hybrid zone along the Elbe represents an example of early-stage speciation followed upon secondary contact between the two emerging species. The classical biological definition of species — which is based on the concept of reproductive isolation, i.e. on the premise that the hybrid offspring of crosses between ‘true’ species are sterile — obviously does not apply in this case. Nevertheless, gene flow is locally restricted in the genome, because each form preferentially mates with individuals of the same color. This in turn means that hybrids with an intermediate color are less likely to reproduce. But the two populations are not yet fully isolated genetically from each other, since hybridization still occurs. “We are now using a mathematical model to work out the level of hybridization in the hybrid zone as it now stands,” says Wolf. “The initial indications suggest that it is very low, on the order of a few percentage points.”

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40 beautiful birds singing, video


This 23 December 2018 video shows these European birds:

1. CHAFFINCH
2. BULLFINCH
3. BLUE TIT
4. GREENFINCH
5. GREAT TIT
6. WREN
7. STARLING
8. HOUSE SPARROW
9. RED CROSSBILL
10. CRESTED TIT
11. WHITE WAGTAIL
12. HAWFINCH
13. MARSH TIT
14. WOOD PIGEON
15. COLLARED DOVE
16. GOLDFINCH
17. LONG-TAILED-TIT
18. GARDEN WARBLER
19. MAGPIE
20. JACKDAW
21. JAY
22. CARRION CROW
23. WILLOW TIT
24. GREAT SPOTTED WOODPECKER
25. BRAMBLING
26. REDPOLL
27. SISKIN
28. GREEN WOODPECKER
29. DUNNOCK
30. NUTHATCH
31. SHORT-TOED TREECREEPER
32. WHITETHROAT
33. LINNET
34. YELLOWHAMMER
35. ROBIN
36. COAL TIT
37. GOLDCREST
38. FIRECREST
39. BLACKCAP
40. ICTERINE WARBLER

Invasive wildlife species to Europe


This 2016 video from South Korea is about Channa argus fish.

From the Centre for Ecology & Hydrology in Britain:

Scientists identify 66 alien species that pose greatest threat to European biodiversity

Invasive animals and plants are likely to arrive in the next decade

December 13, 2018

Summary: Scientists have identified 66 alien plant and animal species, not yet established in the European Union, that pose the greatest potential threat to biodiversity and ecosystems in the region. The research lists the invasive species that are likely to arrive and spread in the region over the next decade.

Scientists have identified 66 alien plant and animal species, not yet established in the European Union, that pose the greatest potential threat to biodiversity and ecosystems in the region.

From an initial working list of 329 alien species considered to pose threats to biodiversity recently published by the EU, scientists have derived and agreed a list of eight species considered to be very high risk, 40 considered to be high risk, and 18 considered to be medium risk.

The research, led by Professor Helen Roy of the UK’s Centre for Ecology & Hydrology and involving 43 people from across Europe and funded by the European Commission, is published in the journal Global Change Biology.

The authors developed a horizon-scanning approach in order to derive a ranked list of potential invasive alien species (IAS). Using this procedure, they worked collaboratively to reach consensus about the alien species most likely to arrive, establish, spread and have an impact on biodiversity in the region over the next decade.

The approach is unique in the continental scale examined, the breadth of taxonomic groups and environments considered, and the methods and data sources used. Species considered included plants, terrestrial invertebrates, marine species, freshwater invertebrates and vertebrates.

The eight species that pose the highest risk are:

1. Channa argus. The northern snakehead is a species of fish native to southern and eastern China but now also widely distributed in Japan within shallow, marshy ponds and wetlands, where it preys on native fish species.

2. Limnoperna fortunei. The golden mussel is native to China and south-eastern Asia but became established in Hong Kong in 1965, and Japan and Taiwan in the 1990s. Subsequently, it invaded the United States and South America. It alters native fauna with an impact on the freshwater food web.

3. Orconectes rusticus. The rusty crayfish, native to the United States but now found in Canada, is a large and aggressive species of freshwater crayfish, which is more successful in deterring attack from predators than other crayfish and therefore outcompetes native species.

4. Plotosus lineatus. The striped eel catfish is native to the Indian Ocean but was first recorded in the Mediterranean in 2002 and subsequently spread rapidly along the entire Israeli coast. This venomous catfish now inhabits all sandy and muddy substrates contributing to species declines through competition and displacement.

5. Codium parvulum. This green seaweed native to the Indo-Pacific Ocean and subsequently described from the Red Sea, has since been recorded off the northern shores of Israel in the Mediterranean and along the Lebanese coast. It is considered an ecosystem engineer, altering the structure and functionality of ecosystems.

6. Crepidula onyx. The onyx slipper snail is native to the southern coast of California and northern Pacific coast of Mexico. It is now widespread and considered highly invasive in Asia where it has been reported from Korea, Japan and Hong Kong. Slipper snails are sedentary filter-feeders and change native ecosystems.

7. Mytilopsis sallei. The black striped mussel described from the Pacific coast of Panama is a brackish species that invaded the Indo-Pacific Ocean during the 1900s and has reached Fiji, India, Malaysia, Taiwan, Japan, and Australia. In some of these coastal areas the species completely dominates since it can survive extreme environmental conditions.

8. Sciurus niger. The fox squirrel native to eastern and central North America, competes for resources with the native western gray (S. griseus) and Douglas squirrels (Tamiasciurus douglasii).

Other key findings include:

  • The highest proportion of the species identified originate in Asia, North America and South America.
  • Aquatic species are most likely to arrive via shipping, while terrestrial invertebrates are most likely to arrive along with goods such as plants.
  • The Mediterranean, Continental, Macaronesian and Atlantic biogeographic regions are predicted to be the most threatened across all taxonomic groups, while the Baltic, Black Sea and Boreal regions are least at risk. The Alpine region appears not to be under threat by any species.

The research provides a basis for full risk assessments that can comprehensively evaluate the threat posed by these species to EU biodiversity.

Professor Helen Roy of the Centre for Ecology & Hydrology said: “Preventing the arrival of invasive alien species is the most effective way of managing invasions. Predicting which species are likely to arrive and survive in new regions involves considering many interacting ecological and socio-economic factors including climate but also patterns of trade.

“Our collaborative approach involving experts spanning many disciplines has been critical to achieve the ranked list of alien species that pose the greatest threat to European biodiversity.”