Tag: adaptation

Guest blog post: Global change, individual behaviour, and trout population persistence

New experiments reinforce that behavioural plasticity can be key for coping with environmental changes

Guest blog post by Daniel Ayllón and Steve Railsback

Early in the morning, Daniel Ayllón and his research mates at the Universidad Complutense de Madrid drive towards the mountains near Madrid. They’re out to survey streams where the endangered Southern Iberian spined-loach and Northern Iberian spined-loach used to coexist. We say “used to,” because once again they fail to find the Northern Iberian spined-loach, probably locally extinct. Such extinctions are not unusual, as freshwater fishes are one of the most threatened groups of animals in the world. There are still many brown trout there, though; the water is still cold enough for them.

Salmonids (trout, salmon and char) are especially challenged by climate change because they need cold, oxygenated and clean water. Trout populations at low altitudes or low latitudes are thus particularly at risk; many in the Iberian Peninsula have been declining for decades as rivers warm and dry. Climate models project a bleak future: such Mediterranean populations will face hotter and drier streams, with more frequent and longer droughts and heat waves, and increasing competition from warm-water fish.

A photo of a brown trout swimming over a bed of smooth pebbles in clear water. — Brown trout (*Salmo trutta*). Photo by J. R. Pérez (AEMS-Ríos con Vida archive)

Despite these changes, local extinctions of trout are still rare, because salmonids are among the most adaptable and resilient of freshwater fishes. They are changing their physiology and phenology, growth and reproduction patterns, and life-history strategies to adjust to the new environmental conditions, via evolutionary, plastic and behavioural mechanisms. While evolutionary ecologists typically focus on genetic adaptation to forces such as climate change, behavioural plasticity could be even more important, because it is fast, reversible and often predictable.

In fact, thermoregulatory movements seem a ubiquitous behavioural mechanism in salmonids: individuals move up and down river networks to find less-stressful temperatures and better growth potential. Behavioural plasticity in circadian activity and habitat selection (deciding when and where to feed) also help trout resist short-term environmental changes. However, we don’t know how important changes in circadian activity─or behaviours in general─are to long-term population persistence in the face of climate change. So to shed light on this question, in a recent work published in Individual-based Ecology, we ran two virtual experiments using the inSTREAM individual-based model to represent a trout population in northern Spain.

A photo of a river flowing between rocky banks, surrounded by greenery and towering mountains under a clear sky. — The Roncal study site on the River Eska (northern Spain). Photo by Benigno Elvira

Steve Railsback and his colleagues at Cal Poly Humboldt University and the US Forest Service’s Pacific Southwest Research Station in Arcata, California, have been developing, testing, and applying inSTREAM for 25 years. The central idea of individual-based models (IBMs) and of individual-based ecology in general is that a biological system can be described through its individual agents, their environment, and the interactions among agents and between agents and environment. The agents of a system (for example, all fish in a population) are modelled as unique and autonomous individuals with their own properties.

The controlled experiment of Harvey and White to quantify how trout trade off feeding vs. predation risk. The experimenters trained wild trout to feed at this dispenser, and then moved it to increasingly risky habitat. The feeding rate needed to keep the trout from leaving increases with the risk it perceives. IBMs like inSTREAM use knowledge about individual behaviour from experiments like this to predict complex population responses. Video by Jason L. White.

Agents also have behaviours: they make decisions, following simple rules or algorithms, independently of other individuals, and seek objectives such as surviving to reproduce in the future. These behaviours are adaptive: agents’ decisions depend on their state and the state of their environment. In this way, population-level results actually emerge from the behaviour of the individuals. In inSTREAM, model trout decide whether to feed vs. hide from predators at different times of day, assumed a trade-off between the need to feed and the predation risk it poses. Temperature has a strong effect on this trade-off because a fish’s metabolic rates, and thus the amount of food it needs, increase sharply with temperature.

A photo of three people wearing waders engaged in field research in a river. — Three members of the research team at the UCM conducting habitat surveys at the Roncal study site. In IBMs like *inSTREAM*, modelled populations and their environment are characterised by field data collected in surveys like this. Photo by Benigno Elvira.

What did we learn with our IBM? First, our simulations show what behavioural ecologists know from experiments: that during warm summers trout can meet their metabolic requirements only by feeding at multiple times of day and segregating temporally, so that fish of different size can feed at the same spot but at different times of day. Feeding during daytime is more profitable but riskier, while doing it at night is safer but less efficient, and feeding during twilight provides near-daytime growth and somewhat-reduced risk.

We then analysed how model trout change their circadian foraging behaviour under increasing climate change. As we expected, trout showed great behavioural plasticity: trout of all ages responded to warmer and drier conditions by increasing daytime feeding and overall foraging activity, although there were differences across age classes in the distribution of daily activity. Our second experiment used a great advantage of IBMs as a virtual laboratory: we can run experiments that are impossible in reality. We tested the importance of behavioural plasticity by simply turning the behaviour off. In our simulations, virtual populations of trout capable of flexible circadian feeding were more resistant to climate change─had higher biomass and a more balanced age structure─than were populations of trout that feed only during daytime.

These experiments reinforce that behavioural plasticity can be key for coping with environmental changes, so we shouldn’t minimise its relevance when predicting the persistence of salmonid populations in warming and drying rivers. This conclusion no doubt also applies to other taxa that have powerful adaptive behaviours.

This study epitomises individual-based ecology, the subject of Pensoft’s new journal: we use what we know from empirical research on individual physiology and behaviour, in an individual-based model, to study complex population responses of direct relevance to our changing world.

Research article:

Ayllón D, Railsback SF, Harvey BC, Nicola GG, Elvira B, Almodóvar A (2025) Behavioural plasticity in circadian foraging patterns increases resistance of brown trout populations to environmental change. Individual-based Ecology 1: e139560. https://doi.org/10.3897/ibe.1.e139560

Life in marine driftwood: The case of driftwood specialist talitrids

Driftwood in the sea – either floating or stranded on beaches – is a common feature particularly in temperate regions. Large quantities of driftwood, termed driftwood depositories, may collect at the mouth of small streams associated with marshes and have been present for some 120 millennia – since the origin of flowering plants.

Once marine driftwood begins to decay, it undergoes a specific succession. Firstly, it is colonized by salt tolerant, wood degrading fungi and bacteria, along with a few invertebrates able to digest wood by producing native wood degrading enzymes. The latter include gribbles (isopods) and chelurid amphipods.

Driftwood hoppers (talitrids), as well as isopods, chilopods, insect larvae, some ants and termites, comprize the secondary colonizers. They are all characterized by their inability to utilize driftwood directly. Instead, they rely on symbiotic microflora for digestive purposes.

Within all talitrids, the driftwood hoppers count as few as seven species, most likely because they are extremely difficult to locate and, therefore, discover and describe. Apart from living in tiny burrows, they measure between 13 and <6 mm, which makes the latter the smallest known talitrid.

Having reviewed the driftwood specialized talitrids, Dr. David Wildish of the St. Andrews Biological Station, Canada, concludes that all seven known species demonstrate dwarfism based on slow metabolism and growth. Their sexual development begins earlier compared to faster growing related species. All of them are also characterized with reduced eye size and absence of dorsal pigment patterns.

In his review article published in the open access journal Zoosystematics and Evolution, the scientist confirms that dwarfism in driftwood hoppers has evolved due to poor diet, in turn resulting in slowed metabolism and growth. A further adaptive challenge is the empty gribble burrow size occupied by talitrids (burrow diameter between 0.6 to 5 mm) with the smaller ones being more widespread. Larger talitrids can only complete their life cycle in the larger burrows.

“The size gradient in gribble burrow diameter provides a satisfactory explanation for serial dwarfism within the driftwood talitrids and is why each species becomes successively smaller,” explains the researcher.

Responsibility for first establishing the driftwood talitrid ecological grouping was made during graduate studies by David Wildish, London University, U.K., and Laura Pavesi, University of Rome, Italy. The two criteria for inclusion of a talitrid in the driftwood grouping was: behavioral fidelity to the occupied driftwood and that the food source was solely rotting driftwood (see references).

The larger talitrid family are small/medium in body length (< 30 mm) crustaceans with more than 400 species described in the world list. Ecological groupings within the family include marine/estuarine supralittoral wrack generalists, sand-burrowing, marsh-living and driftwood specialists. A few freshwater and many terrestrial species are also known.

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Original source:

Wildish DJ (2017) Evolutionary ecology of driftwood talitrids: a review. Zoosystematics and Evolution 93(2): 353-361. https://doi.org/10.3897/zse.93.12582

Trapped in a nuclear weapon bunker wood ants survive for years in Poland

Having built their nest over the vertical ventilation pipe of an old nuclear weapon bunker in Poland, every year a large number of wood ants fall down the pipe to never return back to their colony.

Curiously, although trapped in extremely severe conditions underground, the ants have already upped their numbers to these of big, mature natural colonies, while also carrying on with their basic activities of nest maintenance, constructing and moulding. This unique population is described in the open access Journal of Hymenoptera Research by the team of Polish scientist Wojciech Czechowski, Polish Academy of Science.

The studied colony is still unique, despite the fact that there are previously known similar cases, such as a black garden ant colony that found a home in a chassis of an immobilised car, where the insects had built their nest from mud and dry plant remnants stuck to the underbody. Another wood ant colony is known to have lived in almost complete darkness within a cubic wooden box with no openings apart from a narrow slit at the bottom of one side. Yet, unlike the ants from the bunker, they have all had access to the outside world, having deliberately made their own choice to settle in such extraordinary locations.

Thanks to an yearly campaign set to count the hibernating in the same bunker bats, the ant population was discovered in 2013. Interestingly, when the ants were checked on in 2015, the researchers not only found the population still surviving, but even increasing its numbers.

According to the estimates, they counted at least several hundred thousand workers, arguably close to a million. Moreover, when the researchers went back to the bunker in 2016, they found the mound’s damage, caused on their previous visit, repaired, which showed the population still managed to maintain their nest almost as if they were leading a normal life.

The ant ‘colony’ was found to have built an earthen mound in a small 2.3 m high room with a base area of 3 m x 1.2 m. Normally, such wood ants settle exclusively on large forested islands, where they can forage enough food to answer the high energy demand of the colony.

However, the confined space within the bunker has not been the only obstacle the ants have been facing in their underground trap. Beside the lacking food and light, the ‘colony’ had to also deal with the low temperatures between the one-metre thick ferroconcrete walls. All year long it was no more than 10 °C.

Understandably, the severe conditions within the bunker made reproduction effectively impossible. Although the scientists did undertake a special search for larvae, pupae, empty cocoons or queens, they found nothing. Nor did they find signs of male offspring.

Looking for an answer why the population was still seemingly thriving, the scientists deducted that there was a constant influx of newly fallen ants. The metal plate that once covered the pipe outlet had obviously rusted so much that it has been collapsing under a big wood ant colony’s mound built right over the pipe. In fact, the mortality in the bunker is quite high, but the regular ‘newcomers’ turn out to be overcompensating for the dead ants.

“To conclude, the wood ant ‘colony’ described here – although superficially looking like a functioning colony with workers teeming on the surface of the mound – is rather an example of survival of a large amount of workers trapped within a hostile environment in total darkness, with constantly low temperatures and no ample supply of food,” say the authors.

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Original source:

Czechowski W, Rutkowski T, Stephan W, Vepsäläinen K (2016) Living beyond the limits of survival: wood ants trapped in a gigantic pitfall. Journal of Hymenoptera Research 51: 227-239. doi: 10.3897/jhr.51.9096

New immigrant: Shiny Cowbirds noted from a recording altitude of 2,800 m in Ecuador

Two juveniles of Shiny Cowbird, a parasitic bird that lays its eggs in the nests of other birds, were spotted in the Andean city of Quito, Ecuador, for the first time. This finding represents an altitudinal expansion of approximately 500 m.

Breeding populations might have been prompted by forest fragmentation and/or climate change, suggest the research team, led by Dr Verónica Crespo-Pérez, professor at Pontificia Universidad Católica del Ecuador (PUCE). Resultingly, the ‘immigrants’ could be threatening native birds. The study is published in the open access Biodiversity Data Journal.

“The Shiny Cowbird is native to the lowlands of South America but within the last 100 years, it has been expanding its distribution to higher altitudes and latitudes” says the lead author.

The bird had already been noted from high altitudes in Bolivia and Perú, and in some localities in the Ecuadorian Andes. Since 2000, Juan Manuel Carrión, co-author and director of the Zoo in Quito, recalls observing Shiny cowbirds near his home in a valley near Quito at 2,300 m above sea level (asl). However, one has never before been reported from an altitude as high as 2,800 m asl.

Moreover, the fact that the observed individuals were juveniles means that the species is already breeding in the city.

“Such a significant expansion of reproductive birds, of approximately 500 m, could be related to human disturbances, like forest fragmentation or climate change,” adds Crespo-Pérez.

The observations took place at the PUCE campus about a year ago. Two juvenile Shiny cowbirds were seen parasitizing two different pairs of Rufous-collared Sparrow, one of the most common birds in Quito. The cowbirds displayed food-begging behaviors to adult sparrows, including chasing the sparrows on the ground and chanting intensely on bushes and tree branches.

“These observations mean that the birth mother of the cowbird laid her eggs in the nests of the sparrows, who inadvertently, became the cowbird’s foster parents and incubated, fed and cared for the it as if it were its own, even though the cowbird is almost twice as big,” says Miguel Pinto, co-author and professor at Escuela Politécnica Nacional, and former postdoctoral fellow at the Smithsonian Institution.

“The sparrows were not feeding fledglings of their own species, which suggests that the Cowbird could be having some negative effect on the Sparrow, at least on their ability to reproduce,” points out Tjitte de Vries, co-author and professor at PUCE.

There are several published reports of negative effects of Cowbirds on other birds, especially on species that are already endangered or have restricted distribution ranges. Therefore, this report of an expansion of the Shiny Cowbird towards higher altitudes may be of concern, mainly for native, endemic or endangered bird species.

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Original source:

Crespo-Pérez V, Pinto C, Carrión J, Jarrín E R, Poveda C, de Vries T (2016) The Shiny Cowbird, Molothrus bonariensis (Gmelin, 1789) (Aves: Icteridae), at 2,800 m asl in Quito, Ecuador.Biodiversity Data Journal 4: e8184. doi: 10.3897/BDJ.4.e8184

Huge organs defy austerity for tiny cave snails in the subterranean realm

While most of the knowledge about tiny snails comes from studying empty shells sifted out from piles of dust and sand, the present research is the first contemporary microscopic exploration of organs in cave snails tinier than 2 mm. The paper, published in the open-access journal Subterranean Biology, reveals that underneath the seemingly fragile shells of the Zospeum genus, there are strikingly huge organs.

A number of remarkable observations such as an enormous kidney, grooved three-pointed teeth and a huge seasonally present penis are reported in the recent study, conducted by Adrienne Jochum, Naturhistorisches Museum der Burgergemeinde Bern, Switzerland, and her international team of researchers from University of Bern, Switzerland; Shinshu University, Japan; Universitaetsklinikum Giessen und Marburg GmbH, Germany; Justus-Liebig University Giessen, Germany; University of Ljubljana, Slovenia; University of Bern Goethe-University Frankfurt, Germany; Ruhr University Bochum, Germany; Croatian Biospeleological Society, Croatia and University Duisburg-Essen, Germany.

The scientists describe these characteristics as adaptations the miniature creatures have acquired in order to survive austerity in the subterranean realm.

Usually, adaptations to cave life can include blindness or lack of eyes, loss of pigmentation, sensitivity to changes in temperature and humidity, a high starvation tolerance, or anatomical compromises such as small size and transparent shells. The present study shows that miniscule carychiid subterranean snails have developed huge organs to tolerate the unique conditions of cave life.

“Studying adaptations in extreme environments such as those found in snails of subterranean habitats can help us to understand mechanisms driving evolution in these unique habitats,” explains the first author.

Glassy cave-dwelling snails known only from Northern Spain, the southern Eastern Alpine Arc and the Dinarides might have tiny hearts, but their enormous kidney extends from one to two thirds of the total length of their minute shells. This phenomenon could be explained as an effective mechanism used to flush out large amounts of excess water during flooding seasons in caves.

The same impressive creatures have also developed elaborate muscular plates, forming the girdle that surrounds the gastric mill (gizzard) in their digestive tract. The muscular gizzard grinds the grainy stew of microorganisms and fungi the snails find in moist cave mud. These mysterious creatures graze stealthily using an elastic ribbon (radula), aligned with seemingly endless rows of three-pointed, centrally-grooved teeth, as they glide through the depths of karst caves while searching for food and partners.

Deprived from the hospitable aspects of life we have grown used to, some of the snails discussed in the present paper have evolved their reproductive system in order to be able to reproduce in the harshest of environments, even when they fail to find a partner for an extended period of time.

As a result, not only are these snails protandric hermaphrodites, meaning that they possess male sexual features initially, which later disappear so that the female phase is present, but they have a large retractable, pinecone-shaped penis for instantaneous mating in the summer when mating is most probable. To guarantee offspring, a round sac, known as the receptaculum seminis, stocks sperm received from a partner during a previous mating and allows them to self-inseminate if necessary.

Teeth in these cave snails are also described using histology for the first time. They bear a median groove on the characteristic cusps known for the Carychiidae.

Sketchy, past dissections provide the current knowledge upon which the findings from this investigation are based. Otherwise, historical descriptions of these tiny snails are only known from empty shells found in samples of cave sediment. The genus Zospeum can only be found alive by inspecting cave walls using a magnifying glass.

“Knowledge of their subterranean ecology as well as a “gut feeling” of where they might be gliding about in their glassy shells is necessary to find them,” comments Adrienne Jochum. The authors also emphasize that this groundbreaking work is important for biodiversity studies, for biogeographical investigations and for conservation management strategies.

Adrienne Jochum and her team investigated the insides of the shells using nanoCT to differentiate species in synchronization with molecular approaches for genetic delimitation. Four well-defined genetic lineages were determined from a total of sixteen Zospeumspecimens found in the type locality region of the most common representative, Zospeum isselianum. This investigation is the first integrative study of live-collected Zospeum cave snails using multiple lines of data (molecular analyses, scanning electron microscopy (SEM), nano-computer tomography (nanoCT), and histology.

This work is dedicated to the industrious Slovenian malacologist Joze Bole, whose work greatly inspired the present research.

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Original source:

Jochum A, Slapnik R, Klussmann-Kolb A, Páll-Gergely B, Kampschulte M, Martels G, Vrabec M, Nesselhauf C, Weigand AM (2015) Groping through the black box of variability: An integrative taxonomic and nomenclatural re-evaluation of Zospeum isselianum Pollonera, 1887 and allied species using new imaging technology (Nano-CT, SEM), conchological, histological and molecular data (Ellobioidea, Carychiidae). Subterranean Biology 16: 123-165. doi: 10.3897/subtbiol.16.5758

Bush Blitz: The largest Australian nature discovery project finds 4 new bee species

Four new native bee species were recognised as part of the largest Australian nature discovery project, called ‘Bush Blitz‘. The South Australian bee specialists used molecular and morphological evidence to prove them as new. Three of the species had narrow heads and long mouth parts – adaptations to foraging on flowers of emu-bushes, which have narrow constrictions at the base. The new species are described in the open access journal ZooKeys.

Bees are important pollinators of crops and native plants, but habitat loss and pesticides are proved to be causing a serious decline in their populations in Europe and the United States of America. Meanwhile, the conservation status of native Australian bees is largely unknown because solid baseline data are unavailable and about one third of the species are as yet unknown to science. Furthermore, identification of Australian bees is hampered by a lack of keys for about half of the named species.

With their present publication, bee specialists Katja Hogendoorn (University of Adelaide), Remko Leijs and Mark Stevens (South Australian Museum) are now trying to make Australian native bees more accessible to the scientific community. The study introduces a new Barcoding of Life project, ‘AUSBS‘, which will be built to contain the barcode sequences of the identified Australian native bees.

In future, this database can help scientists who have molecular tools, but insufficient knowledge of bees, to identify known species. Yet, that is not the only use of the database. “Bee taxonomists can access and use the molecular information to answer specific problems, for example, how certain species are related or whether or not a male and female belong to the same species”, says Dr. Hogendoorn. “And combined with morphological information, the molecular database can help to identify new species”, she adds.

In their publication, the researchers demonstrate the utility of the database. After careful evaluation of the DNA sequence data and subsequent morphological comparison of the collected bees to museum type specimens, they recognised four new species in the genusEuhesma, which they subsequently described.

Three of the species belong to the group of bees that specialise on the flowers of emu-bushes. These bees have evolved narrow faces and very long mouth parts to collect the nectar through a narrow constriction at the base of the flowers. A similar evolution has been already observed in other groups of bees. The fourth species belongs to a different group within this large genus and has a normally shaped head.

So far, the project includes 271 sequences of 120 species that were collected during the Bush Blitz surveys, Australia’s largest nature discovery project. The researchers intend to build on the existing DNA database to cover as many as possible of the Australian species. “It is hoped that this will stimulate native bee research”, says Dr. Hogendoorn. “With about 750 Australian bee species still undescribed and many groups in need of revision there is an enormous job to do”, she concludes.

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Original source:

Hogendoorn K, Stevens M, Leijs R (2015) DNA barcoding of euryglossine bees and the description of new species of Euhesma Michener (Hymenoptera, Colletidae, Euryglossinae).ZooKeys 520: 41-59.doi: 10.3897/zookeys.520.6185