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Anthony Montoya

Galapagos Sea Lion Expert

The Galapagos Hawk: The Glass Cannon of the Archipelago

The powerful and intimidating Galapagos Hawk may be looking forward to the future with a sense of unease.
Courtesy of https://commons.wikimedia.org/wiki/File:Galapagos_hawk.jpg

The visible heat waves emanating from the dusty, barren soil serves as an extra, albeit unnecessary, reminder of the other-worldly conditions present on the mystical Galapagos archipelago. Land iguanas make a break for the rock laden breeding grounds, frantically rushing to create underground nests to lay and protect their soon to be territory. Just twenty meters away, a group of Nazca boobies watch curiously, also preoccupied with the rearing of their offspring. Battles occur at points, with sneakier iguanas attempting to steal a nest for their own. Battles mimic a wrestlers scrap, with the combatants rolling and flipping each other, expending dangerous amounts of energy needed to finish their original job quickly. These scenarios are a death sentence for some, as the keen eyed Galapagos hawk may be stalking them at any time. Roaming the sky with deadly intent, the hawk soars and glides, getting closer to the iguanas. From here, they wait to find an unlucky iguana, tired, wounded, or simply at the wrong place at the wrong time. It is at this moment where the deal is sealed, the hawk diving down at breakneck speed, plunging into its prey, killing it instantly in this best-case scenario.

Truly, the Galapagos hawk is the de facto apex predator on the islands it inhabits, taking on an entire ecosystems range of animals, from centipedes and locusts, to snakes and rodents, all the way up to marine and land iguanas (1). Despite their superiority in the air and on land, immense power and intimidating hunting methods, the Galapagos hawk may in fact be one of the most fragile characters in the Galapagos; the inclusion of the smallest foreign microbe could be enough to decimate the species entirely, to shatter a truly vulnerable glass cannon.

This fault, akin to the fault in the Deathstar, is inherent to many species that share the Galapagos hawk’s characteristics; isolated island species that have splintered off from a much larger original population.. While these outcast groups sometimes find a new, optimal habitat where they can thrive, their splintering off from the main group incurs a cost in the form of less genetic variability in the new subpopulation (2).

This concept of a loss of genes in a new, smaller population is known as a genetic bottleneck, and is the culprit for the hawks’ Achilles heel. Think of a soda bottle, two liter, filled with layers of different colored sand, perhaps red on top, then blue, green, and yellow. The bottle as a whole contains a plethora of colors, and if the bottle was shaken, millions of color combinations would be seen. What if the cap was taken off, and only a small amount of sand was allowed out from the opening? If the sand were in layers, only red would come out, and even if the sand was mixed, there would still be a disproportionately larger amount of the top sand layers being represented. If the sand were genes, the new, broken-off population would have only a fraction of gene combinations the main population has, combinations which may have incredibly important traits to them, such as adding immune strength to combat disease.

When a small portion of a large population is isolated and forms a new population on its own, the smaller new group often contains a very different makeup of the original populations overall variance.
Courtesy https://upload.wikimedia.org/wikipedia/commons/c/c7/Founder_effect.png

Back on the Galapagos, scientist Jennifer Bollmer tags and draws blood from these hawks, hoping to compare the genetic makeup with their sister species, the Swainson’s hawk, who believed to have splintered off from each other about 300,000 years ago, a blink of the eye in evolutionary time (3). Luckily, the process of capturing the hawks is easier than expected, not timid to the presence of humans, like many of the other animals in the Galapagos. Bollmer is specifically interested in an area of the genome known as the MHC, or major histocompatibility complex. This is the detector which alarms the immune system that something inside the body shouldn’t be in there, and that it needs to be booted out.

After performing the same gene sequencing technique process to mainland Swainson’s hawks, Bollmer and her colleagues were ready to compare the amount of differing gene combinations within each species. More varied combinations means more markers, which could pick up a larger range of the diseases to act upon. Bollmer’s findings were grim; only three unique sequences were found in 32 total Galapagos hawks, while all of the 20 Swainson’s hawks tested each had their own unique sequences, for a total observed bank of twenty unique combinations. Even worse, the Galapagos hawk would only have at most two combinations present, while their sister species had individuals carrying as many as seven combinations in a single bird; the Galapagos hawk certainly seemed to be in dire conditions (4).

A Swainson’s hawk,banded in a fashion similar to how Bollmer banded her specimens in her research. To the untrained eye, the two hawk species seems to be the same with some slight differences in coloration. The genetic differences between the two,compared  to the appearances, is massive however. Courtesy https://upload.wikimedia.org/wikipedia/commons/e/e6/Buteo_swainsoni_edit.jpg

With an overwhelming amount of human activity and commerce taking place in the Galapagos today, it has never been easier to have an invading germ make the archipelago its home, and some casualties due to this bottleneck is starting to take place to some unfortunate avians of the area. A parasitic fly, Philornis downsi, has decimated certain finch populations due to a feeding process, which would fit right in a horror movie. The larva of this insect feed and destroy upon the nasal cavity of fledging finches, feeding on their blood, and, at worst, killing them, and at best, deforming them severely. “It's a huge burden for the chick,” says Francesca Cunninghame, an ornithologist from New Zealand who works for the Charles Darwin Association (5). These insects were found in mainland South America, but the finches of the Galapagos do not seem to know how to handle these parasites.

The bottleneck issue is definitely prevalent in many island species, affecting not only avians but all types of animals as well. Another high profile animal, the Tasmanian devil, has been victimized by a lack of genetic variability due to the effects of genetic bottleneck, a bottleneck due to our actions. Once stigmatized by humans, these mammals were hunted with no rest for fur up until near extinction in the first half of the 1900’s. Following a change of viewpoints, large rehabilitation efforts commenced in order to boost the population back to a stable number. While successful, the changes in genetic diversity were never taken into account; with only a small population to start of with, the large numbers that are alive today retain very small pools of genetic diversity. Because of this, the entire population is at risk of being wiped out, as a disease which kills one can easily kill all. This scenario unfortunately began playing out in the 90’s were Devil Facial Tumor Disease (DFTD) began occurring throughout all Tasmanian devil populations. The disease, which creates multiple tumors on the animal's face, is almost certainly fatal, and has left the devil in bad conditions once again, and has also left scientists scrambling for a cure or preventative measure (6).

But there still is hope for animals like the Galapagos hawk, the apex predator with a hidden weakness. New gene and DNA diagnostic tools have been developed to allow for individuals qualities to be easily and quickly scanned. With such information available, it is possible for scientists to breed specific animals together with differing genetic makeups to create offspring with a larger amount of variability (7). Slowly but surely, greater variability-and therefore immunological strength-could be obtained, helping the Galapagos hawk to defend itself from invaders. But hasn’t human interaction already stirred up the natural world enough already? At what point do we take our hands off the wheel and let nature take its course? Either way, the iguanas will be intently watching what we decide to do.

For now, the Galapagos hawk continues to soar above the enchanted archipelago, weary, but strong. Courtesy of Nick Fletcher

References:

1.Licon, Daniel. "Buteo galapagoensis: Galapagos Hawk". University of Michigan Museum of Zoology Animal Diversity Web. 2008. 5 Mar 2008 <http://animaldiversity.ummz.umich.edu/site/accounts/information/Buteo_galapagoensis.html>.

2.Frankham, R. "Do island populations have less genetic variation than mainland populations?." Heredity 78.3 (1997).

3.Whiteman, Noah Kerness, et al. "Disease ecology in the Galapagos Hawk (Buteo galapagoensis): host genetic diversity, parasite load and natural antibodies." Proceedings of the Royal Society of London B: Biological Sciences 273.1588 (2006): 797-804.

4. Bollmer, Jennifer L., et al. "Reduced MHC and neutral variation in the Galápagos hawk, an island endemic." BMC evolutionary biology 11.1 (2011): 1.

5. http://www.galapagosdigital.com/2014/05/29/rescuing-the-mangrove-finches-great-first-step/

6.Hawkins, Clare E., et al. "Emerging disease and population decline of an island endemic, the Tasmanian devil Sarcophilus harrisii." Biological Conservation 131.2 (2006): 307-324.

7. Milinkovitch, Michel C., et al. "Genetic analysis of a successful repatriation programme: giant Galapagos tortoises." Proceedings of the Royal Society of London B: Biological Sciences 271.1537 (2004): 341-345.