Male fence lizards (Sceloporus undulatus) have bright blue patches, or “badges”, on their chin and abdomen (see pic). They show these off to rival males and potential mates by doing little push-ups, which allows the blue to be seen from a distance. We tested whether the physiological consequences of stress (in particular, elevation of glucocorticoid hormones) results in a) badges being less colourful, and b) male lizards showing off their badges less (i.e. doing fewer push ups, at elevations where they would be less visible). We found that overall, elevated stress hormone levels did not result in changes to badge colour, or to display behaviour.
Co-author Gail McCormick did an excellent job writing up this research for Penn State Science – check it out here for more information.
In case you haven’t noticed, it’s been an unusually mild winter in most parts of the United States. How mild? Well, for the first time in 146 years, Chicago had no snow in January and February (38 years longer than they went without a World Series win, not that anyone was counting) – and in Miami, temperatures never once dropped below 50˚F, a first in recorded history (and they’ve been keeping records there for 121 years). Although the north west saw record cold, far more weather stations (8% in fact) recorded the HOTTEST winter on record.
To put this in perspective, the record for “warmest winter” in the Lower 48 states was held by – you guessed it, the winter immediately before this one (2015/16). And this is part of an upward trend in winter temperatures, not just a 2-year fluke:
Looking at the top graphic, the south east region of the US (where I conduct my research on eastern fence lizards) was particularly warm this winter. This area is an important hotspot for reptile and amphibian diversity, and as I’ve been working on reptiles in particular, these interesting (and worrying) trends have had me thinking about how warm winters might affect reptiles.
Reptiles are ectotherms, meaning they depend on external sources of body heat, and have limited ability to physiologically control their own body temperatures. Maintaining an optimal body temperature is therefore very environmentally-dependent in these species. This is thought to make them particularly vulnerable to the effects of climate change.
Elegant work done by Barry Sinervo and colleagues (published in Science) suggests that increased global temperatures will lead to a reduction in reptilian diversity because as temperatures increase, reptiles are limited by their upper temperature limits. Every reptile (and animal generally) has a “critical thermal maximum/minimum” – these are the upper and lower temperatures beyond which physiological processes will cease and they will die. So, if it’s hotter, reptiles can spend less time being active and foraging, and have to spend more time resting in the shade to avoid reaching critical thermal max. This will have effects on their body condition, ability to reproduce, and ultimately, on population growth, leading to increased likelihood of extinction.
So it’s pretty obvious how warmer SUMMERS could impact reptiles, by pushing them more frequently to their critical thermal maximum, and forcing them to adjust their behaviours to avoid this. But, what about warmer WINTERS?
My hunch was that warmer winters probably interfere with regular over-wintering behaviours in reptiles. But when I started to dig into this topic I found that what a “regular” over-wintering behaviour is in a reptile is highly variable, even within species. Some species, like rattlesnakes (see pic), go into hibernation much like a bear or a small mammal – though when they do this, and for how long, is highly dependent on their latitude. To generalise, reptiles at least “power down” for the winter months when food is relatively scarce: they lower their metabolism to conserve energy, and may burrow underground or move into crevices, which is why they’re usually hard to spot during this period.
I work on the eastern fence lizard, Sceloporus undulatus, which is a widely-distributed species, occuring from Mississippi to southern Pennsylvania. We don’t know much about over-wintering behaviour, but we do know that they come out when it’s warm, even if that’s in the middle of winter:
Although they are likely to display variation in over-wintering behaviour given their huge latitudinal range, seeing them out and about this early in central Arkansas is definitely unusual.
But – should we be worried to see little Scelops out in late January or February? Are warm days at this time of year going to do them any harm? Temperature increases during the winter are surely likely to fall well between critical thermal min & max, and if anything, should result in temperatures that are closer to each species optimum (the smaller range of temperatures that ectotherms will seek to achieve, at which physiological processes, such as digestion, are optimised). So, do warmer winters matter?
The short answer is yes, it probably does, and it’s probably not great news for reptiles like the fence lizard.
There are a couple of reasons why. First, becoming active in winter requires upregulation of the animal’s metabolic rate, which has been lowered for the winter period. Our metabolism, amongst other things, is the suite of processes that convert food/fuel to usable energy to allow us to be active. Metabolic rate is highly sensitive to temperature in reptiles, so as it gets warmer, they start burning through their energy stores. Remember, there’s a reason that reptiles go into a state of reduced metabolism during winter: there’s less food around! Especially for those that rely on hibernating mammals, but also those that need to eat lots of insects that are less plentiful when it’s cooler, like lizards. So, becoming active and increasing your metabolism is probably a bad thing when it’s going to burn up your stored energy, and there’s limited potential for you to recoup it by finding lots of food.
A number of studies have found that milder over-wintering temperatures result in decreased body condition come Spring-time, and higher levels of physiological stress, as a result of this increase in metabolism. For example, painted turtles that experience just a 5˚C increase in winter temperatures use almost twice as much energy (Muir et al. 2013); and aspic vipers had reduced Spring body condition after being kept at 14˚C instead of 6˚C (Brischoux et al. 2016).
There’s another reason that “milder” temperatures are likely to be bad news for reptiles (and other animals too): they may be high enough to promote activity, but still low enough to result in impaired digestion, performance etc. Remember the optimal range of temperatures that maximise physiological performance? For Sceloporus lizards, that range centres around 30˚C. So, they have to reach this temperature, or close to it, to be able to digest food properly. In other words – mild temperatures of, say, 16-22˚C may be enough to fire up the engine, but not get it working efficiently, which can lead to problems like this:
Winter heat spikes cause issues for alligators- resume feeding, gets cold again, temps 2 low to digest food->die
As well as digestion, other aspects of physiological “performance” may suffer at low-mild temperatures, such as sprint speed. As you can see in this figure, endurance (minutes on a treadmill) and especially sprint speed (centimetres moved per second) in Sceloporus lizards (both things that are likely to be important in escaping a predator, or trying to catch a food item) are maximised above 26˚C, and reduced below 20˚C.
from Angiletta et al. 2002.
So, to sum up my non-expert forays into thermal biology of reptiles and answer my initial question: yes, increased temperatures during the winter period most likely do matter. To summarise:
mild temperatures are likely to bring reptiles out of torpor
this necessitates/is accompanied by an increase in metabolic rate, which uses stored energy
furthermore, food availability is likely to be lower at this time
and their digestion/other physiological processes are impaired at these temperatures
with the result that they are in lower body condition when the Spring finally rolls around.I’ve really enjoyed diving into the thermal ecology literature out of interest to know how the warm winter we’ve been experiencing will affect my study species. But this is outside my realm of expertise! So, if you’re interested in this topic, here are some great Twitter accounts to follow for people who know far more about this than me:
Muir et al. 2013. Journal of Thermal Biology. Energy use and management of energy reserves in hatchling turtles (Chrysemys picta) exposed to variable winter conditions. http://www.sciencedirect.com/science/article/pii/S0306456513000557
Social monogamy in mammals evolved in solitary ancestors to allow males to monopolise widely-spaced females, says new research from the Department of Zoology.
Dr Dieter Lukas led the comparative study alongside Professor Tim Clutton-Brock, a renowned expert on mammalian social systems and principal investigator of the Kalahari Meerkat Project.
Their research, published in Science, shows that monogamy, a system in which a single male associates permanently with a single female, evolved as a mating strategy where males were unable to monopolise and defend multiple females over large territories. It did not evolve, as has been thought, due to a need for extra offspring care from the father, which most likely arose as a consequence of monogamy itself.
Lukas classified the social system of all mammalian species for which information exists, a sample of two and a half thousand species. He found that nine percent were socially monogamous, including large carnivores like jackals and wolves, and a number of primate species. This is much lower than estimates of the extent of social monogamy in birds, where it occurs in about ninety percent of species.
“Previously there have been different ideas about the evolution of social monogamy in mammals,” says Lukas. “With this study we were able to test all these different hypotheses at once.” Their first finding was that monogamy arose in species where individuals were solitary and rarely interacted except to breed. They were also able to dispel previous hypotheses regarding the evolution of monogamy, an advance that was possible, says Lukas, due to the volume of information they collected.
Monogamy was thought to be possibly linked to a need for the male’s support in raising offspring, for example, if the female alone could not provide enough food or adequately defend the young. This study shows that paternal care evolved after monogamy was already present. “With the amount of information that we had, we were able to really pinpoint when these transitions happened, and which happened first. Paternal care indeed evolves after monogamy is present, and seems to be a consequence. It seems to occur in about half of all socially monogamous species, and once it does evolve it provides clear benefit to the female.”
They found instead convincing support for the hypothesis that monogamy arose as a mating strategy where males could not defend access to more than one female. This is linked to population density, and indirectly, to diet. In species where social monogamy evolved, females are dispersed widely. Lukas and Clutton-Brock found that while monogamous and non-monogamous species do not differ much in female home range size, monogamous females defend their territories much more vigorously from other females.
This most likely comes down to the density of food, which determines the level of competition, and the benefits of territoriality. The study found a link between monogamy and species that rely on patchily distributed but high quality food sources, such as meat and fruit. Many carnivores, consequently, are monogamous – herbivores, which rely on low quality but widely distributed food sources such as grass, tend not to be.
Where females are spaced far apart, males cannot guard more than one. “If females are dispersed really widely,” says Lukas, “then the best strategy is to stick with her, defend her, and at least make sure you sire all her offspring. In short, the best strategy is to be monogamous.”
The analysis did not include humans, and Lukas believes that the complications of human culture may provide further reasons for monogamy in Homo sapiens. “There is a huge debate as to what the social system in humans actually is – monogamy seems to be pretty widespread these days, but we don’t, for instance, know how widespread it is in indigenous populations. Another thing that’s peculiar about humans is that we have pairs that live within larger groups, something we don’t observe in any other mammal. This makes it really difficult to understand whether what we observe in humans is parallel to what we observe in other mammals, which is unlikely to be the case.”
[I wrote the University of Cambridge press release – this is the pre-edited draft version]
In the news today, this piece by Steve Connor brings up a lot of the issues surrounding the ethical use of GM crops in Africa that I spoke about last July in my coverage of the Crop World Global Conference.
In sum, (in Connor’s words):
Professor Calestous Juma, a Kenyan-born expert on sustainable development, warns that vital improvement in food production that could help to feed a rapidly expanding population in Africa is being held back by anti-GM legislation designed to placate environmental activists in Europe.
Unfortunately, my article never went to print. Here’s the copy, though, as it seems that little has progressed since then.
Ahead of his keynote speech at the Crop World Global Conference this week, Kenyan scientist and governmental agricultural advisor Felix M’mboyi slated the “hypocrisy and arrogance” of the European Union’s opposition to genetically modified crops. This stance, he says, is crippling the development of biotechnology in Africa, which he argues could provide the continent with a chance to feed itself.
Europe’s resistance to GM is hardly a new issue, but M’mboyi’s remarks are especially relevant as the population crisis once again comes to the fore once in light of the UN’s predictions that the global population could more than double to hit 15 billion by 2100. The Observer’s estimates of a population of 9.6 billion in 2050 indicate that almost a third of those will live in Africa – the world’s poorest continent.
That Europe’s negative attitude to GM crop production, reflected in notoriously prickly EU legislation, influences legislators and research funding organisations in the third world is undeniable. Bans on GM imports make their research and development an extravagance in most African countries – even where there are no crop exports, countries’ support of GM crop cultivation most commonly follows European policy. The most heart-rending example of this influence came in 2002, when in the midst of a food crisis Zambia turned away tonnes of food aid from the USA because it could not be certified as GM-free.
This mistrust of genetically modified foods may sound histrionic in the face of such calamity, but it is a mirror of the same deep suspicion found throughout progressive Europe. One doesn’t need to look deeply into British anti-GM literature to find phrases like “monster crops” and “Frankenstein food”, rhetoric more suited to a synopsis of “Little Shop of Horrors”. Given how much of our lives in the first world is now governed by the use of technology it seems somewhat medieval to hold plant biotechnology in such suspicion, even despite the admitted domination of the industry by giants such as Monsanto.
The textbook example of gene technology’s contribution to food security in developing countries is “Golden Rice” technology, developed and donated for humanitarian use by German plant scientists Peter Beyer and Ingo Portrykus. Through the insertion of two genes into the rice genome, greatly increased quantities of β-carotene, a form of vitamin A, deficiency in which is responsible for thousands of preventable deaths in developing countries, are produced and accumulated in the grains. Such research clearly proves that genetic modification of crops can be massively beneficial without the need for reliance on shady multi-nationals, and with no controversial health or environmental side-effects.
The potential hazards that campaigners in Europe base arguments on, like hybridisation with native varieties or possible (but so far unproven) risks to humans via consumption, seem minor compared to predominantly African problems like starvation and malnutrition, which could be alleviated by GM crops which guarantee higher yields. Furthermore, crops which are modified to be resistant to insects will reduce the use of pesticides, reducing the process of chemical soil leaching and run-off into waterways – as well as reducing the impact of agriculture on insect populations. These are all valid points in Europe, but in Africa where people die daily because of toxins in poorly treated (or completely untreated) water, this one example feature of GM crops could save lives even beyond the simple increase in yield.
In Britain and much of Europe we may be right to champion organic and sustainable farming practises for ethical reasons – with no risk of a food deficit, we have the luxury of choice. But what is appropriate to prioritise in Europe is clearly not the same as what needs desperately to be prioritised in Africa. If this year’s famine in East Africa is an indicator of what is next, the food crisis will begin in Africa, and Dr Felix M’mboyi has made it clear that Africa is seeking its own solutions. If his criticism of Europe’s stance on GM crop production is not unfounded, it may be that the best pre-emptive aid we can supply is a rethink of our attitude.
A little while ago I wrote this post in response to an article by Tim Caro and Paul Sherman about why behavioural biologists avoid involvement in conservation science. You can read about my thoughts on the divide that Caro and Sherman highlighted between theoretical and applied science here, but our conclusions were the same: that,
“many studies of animal behaviour are relevant to solving conservation problems, and we therefore encourage behaviourists to contribute more strongly to finding practical solutions to the contemporary conservation crisis.”
Never heard of the Kōkako? Neither had I until this morning – but it has a distinguishing feature that will ensure you remember it. Check out this video (courtesy of BushTellyTV) and listen out for its call: like a cross between a harmonica, and a creaky window…
This beautiful songbird is found only in New Zealand. Like many of New Zealand’s endemic birds that have darted around the forest floor for hundreds of years, it has suffered from the introduction of ground-dwelling carnivores like rats and possums, as well as substantial habitat loss. Currently there are only 22 populations – 11 surviving, and 11 reintroduced.
The ability to successfully translocate individuals of this species is therefore crucial to its survival. This paper looks at the success of translocation in a source population, and two translocated populations in the North Island of New Zealand, by investigating the effect of translocation on song.
The importance of song for mate attraction and territory establishment in bird species has been well established; likewise, spatial variation in song patterns is a known phenomenon. But how might local song diversity affect the success of translocation attempts? If there is variation in song structure between translocated populations, and each population has a preference for its own song, the resulting divergence could lead to a reduction in gene flow and genetic diversity. For the endangered kōkako, this could do more harm than good.
The study found that in the three populations (the source population, and the two translocated populations), song structures and phrasing differed significantly, suggesting the potential for these populations to diverge in preference. Luckily for the future of translocated kōkako, however, there didn’t seem to be discrimination against foreign songs when individual birds were played songs of birds from the same, and different locations.
This is good news for the conservation of the species, as continued introductions of new birds is important for population persistance, as it maintains a healthy level of genetic diversity. The authors suggest, however, that introduced birds should be from as close to the original population as possible to maintain cultural homogeneity.
Overall, despite songs diverging over distance, the kōkako is on track for a successful translocated future. Worth making a song and dance about.
Police in Sheffield were able to catch a teenage burglar in the act using methods derived from optimal foraging theory – exactly where mathematical modelling predicted he would strike next.
Optimal foraging theory suggests that organisms forage in such a way that their food intake per unit time is maximised – for example, by exploiting all possible resources in one food patch before moving on to the next, thereby getting as much food as possible in the shortest time. This saves energy, making the net value of their food intake higher because they have expended less to get it.
Using this theory, the South Yorkshire police force could predict that the burglar, who had already notched up twelve successful burglaries in the area, would stay within the same neighbourhood. Science was proved right; the burglar was apprehended last month, and has since pleaded guilty to twelve counts of burglary, confessing to stealing and selling on laptops, electrical equipment, jewellery and cash.
American series “Numb3rs” depicts a team of brothers in the US Police Force cracking cases by using scientific theory and mathematical modelling to predict the movements of criminals – who would have predicted that it would be the bobbies of South Yorkshire who would prove it to be not so far-fetched…
And if we can catch criminals using science, then surely listening to the advice of scientists to do something as vital as saving Britain’s bees shouldn’t be too much of a stretch? Let’s hope so – a picture article in the Guardian today (with research from the University of Reading) suggests that our rarest bees are in steep decline. The UK opposed the recent ban on nicotinoid pesticides on crops attractive to bees that was passed through at a vote in Brussels. Critics of the legislation said that more research needed to be done to ensure that this wouldn’t have knock-on effects, for example, farmers reverting back to more harmful chemical pesticides. Many scientists and campaigners are saying that it’s time to use what we know. Time is running out for species like the Great Yellow Bumblebee, which is now restricted to the north west of Scotland. By the time further, more speculative research is done, it might be too late.
Dr Kirsty MacLeod 