Galapagos Marine Iguana: Genes and Islands

The Galapagos never cease to fascinate. New discoveries are being made all the time on the animals that live there and how they have evolved. 

Marine Iguana. Santa Fé
(Barrington) 

I watched Marine Iguanas (Amblyrhynchus cristatus) for hours when we there in 2012: lekking behaviour, males fighting, mating, salt glands in action, feeding on algae, and just sitting around on rocks in large numbers.

Marine Iguanas vary in appearance between the islands and those with an obsession for artificial pigeonholes have created subspecies accordingly. I shall ignore those dated divisions and concentrate on a recent paper* in which mitochondrial and nuclear DNA sequences have been used to investigate the population genetic structure.

This paper has highlighted the tendency towards the splitting into different species—speciation—and the hybridization between lineages that tends to wipe out that tendency. While the split between the Galapagos Land Iguanas and the Marine Iguana was calculated to have occurred 4.5 million years ago, division into genetic lineages in the Marine Iguana was found to be very recent—within the last 50,000 years.

As well as differences between islands, different lineages were even found on one island: San Cristobal or Chatham as it was known in Darwin’s day, and to some of us still is. It is presumed that volcanic events, with their huge lava fields divided the populations at some stage; there was a major eruption 1800-3000 years ago which reduced the population and produced a severe bottleneck in both lineages. What is surprising is that migration and hybridization between these two populations, termed LO (for Lobería in the south-west of the island) and PP (for Punta Pitt in the north-east) was uncommon despite there being only 12 km of coastline between them. However, evidence was obtained for hybridization of both LO and PP lineages with animals from other islands rather than the adjacent population. Indeed, migrants were found from Santa Cruz (Indefatigable) and Espaniola (Hood) during the collection of samples. Therefore, introgression of genes from other populations acts to oppose the isolation that would tend towards speciation.

Marine iguana population clusters and phylogenetic relationships. (a) Map of the Galápagos archipelago with major islands colour-coded according to their marine iguana population cluster assignment inferred from structure analysis of 614 individuals genotyped for 12 microsatellite loci (vertical panel in (b)). (b) Species tree cloudogram based on an analysis of 6257 RADSeq-derived SNPs in 33 marine iguanas from across the archipelago, including both San Cristóbal lineages. The graph shows the posterior distribution of consensus trees. Asterisks mark nodes with posterior probability = 1.0 (all other nodes less than 0.9). Specimens were grouped according to population assignment based on structure analysis. From MacLeod et al. 2015

Genetic and morphological differentiation of LO and PP lineages on San Cristóbal Island. LO-SRL and PP-SRPC refer to the original Lobería and Punta Pitt localities, photos show adult LO and PP males. (a) Assignment of 454 individuals based on 18 microsatellite loci, after exclusion of inter-island hybrids and migrants. Abbreviations show sampling locations and 1993 marks specimens sampled in that year. (b) Haplotype network of control region sequences (mtDNA) for LO and PP specimens. (c) Map of sampling localities; arrows indicate migrants/hybrids from Santa Cruz (green), Española (orange) and Lobería (blue); dagger symbols denote locations of within-island hybrids between PP and LO; triangles denote locations of inter-island hybrids. Population SRECA contains Española migrants/hybrids only. Shaded areas mark lava groups 4–6 aged less than 0.1 Ma [40]. (c) Mean, standard deviation and range of morphological variables differing between LO and PP. ***p < 0.001, **p < 0.01, *p < 0.05; sample sizes above each plot, details and abbreviations in Results and electronic supplementary material. From MacLeod et al. 2015

There are differences in size between lineages, PP for example, being smaller than LO, but I will leave consideration of the significance of that and to what happens during El Niño oscillations, when food in the form of algae is short and the populations of Marine Iguana crash, to another time.

We only visited the south of Cristobal, so saw just those of the LO lineage. The question then, of course, is: which ones did Darwin see when he collected on Chatham (named, like Punta Pitt, after William Pitt the Elder, 1st Earl of Chatham, 1708-1778)? LO, certainly, in the south where there are groups of iguanas around Cerro Brujo, for example, but it is likely that he also saw PP, since some of his landing and collection points were well to the north and within the PP lineage’s range^†.

The photographs shows Marine Iguanas from some of the islands we visited:

Española (Hood)

South Plaza

Isabella (Albemarle)

Fernandina (Narborough)

The extent of the lava fields can be seen in this photograph taken on Isabella between from near Darwin Volcano to the south east:

A close-up of the lava on Santiago (James):

…and these are three videos, all taken on a wonderful morning on Fernandina (Narborough):

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*MacLeod A, Rodríguez A, Vences M, Orazco-terWengel P, García C, Reillmich F, Gentile G, Caccone A, Quezada G, Steinfartz S. Hybridization masks speciation in the evolutionary history of the Galapagos marine iguana. Proceedings of the Royal Society. B 282, 20150425.

†Estes G, Grant KT, Grant PR. 2000. Darwin in Galapagos: his footsteps through the archipelago. Notes and Records of the Royal Society of London 54, 343-368.

Hedgehog Oil

Hedgehogs (Erinaceus europaeus) are said to be getting less common in Britain—hardly surprising news given the increase in the human population, the horizontal expansion of cities, towns and villages and the hard landscaping of gardens and public areas. The increase in the number of badgers which prey on hedgehogs is also being blamed.

View image | gettyimages.com

The hedgehog population is these days though safe from organised human predation. I get bemused looks from my family when I tell them that the treatment in the 1940s and 50s for hard ear wax was hedgehog oil. From internet searches one may be left with the impression that hedgehog oil was used by country bumpkins who knew no better and who in turn had copied its use from the gypsies, as in this report from the Western Gazette of 11 March 1938:

Teddy Johnson, a 71 years-old recluse was on Sunday found dead in his small hut of earth and tins, near Swepstone, Ashby-de-la-Zouch, Leicestershire, where he had lived for 25 years. His past life was a secret he kept to himself. He sold watercress and an oil extracted from hedgehogs, which countryfolk regarded as a cure for deafness…

A Mrs O’Dell was singing its praises in Luton News and Bedfordshire Chronicle of 20 July 1950:

The oil from the hedgehog is the finest stuff in the world for earache. It has been worth a lot to me, with a family, as we could not get olive oil in war-time.

     My mother-in-law used to skin them, cook them slowly in the oven and strain off the oil. The hedgehog is a tasty dish.

     The gipsies like them and it was the gipsies who told us to use them for their oil.

Its use was, however, far more mainstream; hedgehog oil came in small bottles from regular pharmacies. The bottle and its contents would be warmed to body temperature in water or in front of the fire before the oil was run into the ear from an eye dropper. Olive oil and proprietary preparations gradually took over; and remember that was the only use olive oil had in the 1950s—if somebody had suggested cooking with it or even eating it with bread, they would have been seen as quite mad.

Searching for information on hedgehog oil is complicated by the fact that ‘Hedgehog’ was used as a brand name for lubricating oil by W.B. Harrison, a ship chandler, of Sunderland. 

The question is, of course, why was hedgehog oil so successful? It was liquid at room temperature and, unlike fish oil, had no unpleasant smell. The adipose tissue of domesticated animals is too hard at room temperature to be used. The melting point depends on the fatty acid composition and, yes, hedgehog fat has been analysed* and it is possible to see from the results why it can produce when rendered an oil at room temperature that is effective at softening cerumen and relieving the pain of hard wax.

…And you take this as a report from a satisfied user circa 1949.

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*Laukola, S. 1980. Seasonal changes in the fatty acid spectrum of the hedgehog’s white and brown adipose tissue. Anal. Zool Fennici 17, 191-201.

The great fall of migrants on the Suffolk coast in September 1965; we were there

Male Bluethroat (Luscinia svecica)
photographed in Moscow
(from Wikipedia**)

Last month marked the 50th anniversary of a remarkable wildlife phenomenon on the Suffolk coast in the east of England. And we were there at the time.

As we approached the coast at Benacre on foot, we suddenly noticed that there were lots of birds around and that these birds were not the usual birds one might expect to see. In short, the shrubs and bushes were full of migrants and rare migrants at that. One bush had Bluethroats on nearly every branch and a Wryneck in the middle. There were Redstarts; Pied Flycatchers were abundant and a variety of small warblers skulked in the low shrubs and bushes. It was an amazing sight. Wherever we walked there were more and more birds.

A few days later when we returned they had all gone.

The ‘fall’ of migrants made the local weekly newspaper because Lowestoft, the town to the north, had been brought to a halt as exhausted migrants landed on buildings, roads and paths. in a post on Birdforum from 2008, a correspondent quoted from Birds and Weather: A Birdwatcher’s Guide by Stephen Moss (Hamlyn, 1995):

At just after two o'clock in the afternoon of 3rd September 1965, the residents of Lowestoft looked up to see a vast cloud of small birds overhead. Birds were dropping out of the clouds like raindrops, and soon the town was alive with them, in gardens, on the beach, and even in the roads, where many fell victim to traffic. Two people, in different parts of the town, actually had Redstarts alighting on their shoulders from the sky.

     Tens of thousands of birds were involved. All along the Suffolk and Norfolk coasts, great flocks of Northern Wheatears and Whinchats, Redstarts and Pied Flycatchers, Garden and Willow Warblers were arriving exhausted from the North Sea, and landing anywhere they could find food and shelter.

     The following morning, one observer, David Pearson, walked along the coast south of Walberswick. Along a 3-km stretch, he logged a staggering total of 15,000 Redstarts, 8,000 Northern Wheatears, 3,000 Garden Warblers, 1,500 Whinchats, 1,500 Tree Pipits, and 1,000 Willow Warblers, along with smaller numbers of other migrants. Rarer migrants were seen in unprecedented numbers, too: Wrynecks and Bluethroats reached double figures in several places, with Icterine and Barred Warblers, Ortolan Buntings and Red-backed Shrikes also appearing.

     The species involved and the time of year, left the lucky observers in no doubt that they were witnessing a massive displacement of Scandinavian migrants which, heading south-south-west across the North Sea to the coasts of mainland Europe, had been diverted westwards to East Anglia by the adverse weather conditions.

British Birds (59, 353-376) in 1966 carried an article by Peter Davis, then Migration Research Officer at the British Trust for Ornithology, entitled, ‘The great immigration of early September 1963’. It describes what was being seen by observers and ringers along the east coast of the British Isles over the few days in early September together with the weather maps. During the last few weeks of August there had been cloud and rain over Scandinavia. On 2 September there was an anticyclone over Scandinavia, creating ideal conditions for the birds to leave in very large numbers; at the same time there was a vigorous depression moving from France into the North Sea, bringing a north-easterly to easterly wind together with heavy rain on the northern edge of the depression, towards the Suffolk and Norfolk coast during 3 September. The migrants were pushed westerly and arrived in the massive falls recorded during the period of heaviest rainfall.

The fall of migrants was described as by far the heaviest of its kind ever recorded in Britain.

What we did not know when we were at Benacre was that a bird ringer was at work there. Davis reports:

…at Benacre Pits, most of the birds appeared between 13.20 and 13.50 GMT, many thousands arriving along a half-mile front. Pied Flycatchers and Redstarts were the most abundant, but there were huge numbers of Wheatears, hundreds of Whinchats, Garden Warblers and Willow Warblers, smaller numbers of Spotted Flycatchers, Tree Pipits, Whitethroats and Robins, and at least 20 Wrynecks. Between the start of the arrival on the 3rd and early on the 5th (when he ran out of rings) A. G. Hurrell^† caught some 650 migrants there, of which half were Pied Flycatchers (a much higher proportion than was seen at other places); also included were 14 Wrynecks, two Bluethroats, three Icterine Warblers and an Ortolan Bunting. 

Benacre Pits was part of the area we explored (probably on the afternoon of the 5th; we have no record). I think the Bluethroats must have avoided his nets since we saw many tens of individuals.

I should point out that Benacre has changed markedly through coastal erosion over 50 years. We walked down the same path to the beach a few years ago and found the chunk of land containing the bushes and scrub where we had seen most of the migrants had gone. We could not remember there being the cliff line then and I have just read in a blog that there was no cliff line here at all until 1981 ‘rather a gradually descending warren which over the years has been subsumed to the sea’.

Also gone were the Suffolk Punches, surely the most attractive of the draught horses, that lived in a field to the right of the path*.

This map from a modern Google Earth view was where we walked; it lacks the land that has disappeared into the North Sea between the end of the path and the beach. The point of the arrow shows where we first noticed that the bushes were full of birds.

Having seen the result of that massive fall of migrants, completely by chance, we have turned birdwatchers green with envy over a period of 50 years.

†Later Sir Anthony Hurrell, noted amateur ornithologist and bird ringer; a civil servant in the Ministry of Education for a time he was later British Ambassador to Nepal (1983-86). He died on 19 April 2009, aged 82.

*Were these the ones reported to have been used as two teams for ploughing, harrowing and towing balers on the Benacre Estate up to 1995? There area number of references to Suffolk Punches with Benacre in the name in studbooks and pedigrees.

**By Bogomolov.PL (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons