New boundaries: Redefining the geographical range of a threatened fish through environmental DNA survey

Accurate data on the distribution and population status of threatened fish species are fundamental for effective conservation planning and management. In this work, in order to reassess the distribution of the globally threatened Evia barbel, Barbus euboicus, we undertook an environmental DNA (eDNA) survey coupled with conventional electrofishing, focusing on major river basins in Evia Island in proximity to its known occurrence in a single Evian basin (Manikiatiko stream). For comparison purposes, we conducted eDNA sampling in several locations in the geographically closest continental river basin, the Sperchios basin (Central Greece) which hosts the closely related Barbus sperchiensis. Our results expand the known range of the Evia barbel on Evia adding four new river basins, apart from its type locality (Manikiatiko stream (EV3)). In a single Evian River, where the species had never been located before, there was also a positive eDNA signal for Barbus sperchiensis within the same basin. The research confirms the occurrence of Evia barbel in a wider geographical area, highlighting however the sensitive conservation status of the species due to its still very narrow geographical distribution. The biogeographical implications of our study, as well as potential conservation interventions, are discussed

Vroege omgeving en de ontwikkeling van sociaal gedrag van de Trinidadiaanse guppy, Poecilia reticulata

One of the many advantages of group living is the swift transfer of information between group members. Social learning – learning from others – offers a quick and economical way to acquire information about the local environment and is considered adaptive under a wide range of circumstances. However, social information can be unreliable or quickly become outdated in rapidly changing environments. Thus flexibility in the utilization of social learning, depending on the associated costs and benefits, would be expected to be advantageous in most situations. Early environment plays a major role in shaping the morphological, physiological or behavioural phenotype of an animal, and conditions and experiences during early life can potentially prepare (or program) a developing individual for the environment it will encounter when adult. In this thesis we examined whether social behaviours such as grouping and social learning could be influenced by early life conditions and to what extent. For this purpose, we used two different strains of the guppy (domestic and wild-origin), Poecilia reticulata, a popular study system in behavioural and evolutionary ecology with well-described social behaviour. In the study presented in Chapter 2, we investigated whether grouping tendencies and social learning propensities were consistent and heritable traits. First, we tested individuals in similar social learning and shoaling tests to assess individual consistency in their performance. We found evidence for consistency in the male subjects’ shoaling behaviour but not in their social learning propensities. We found no evidence for individual consistency in the case of females. Subsequently, we paired male and female subjects at random, obtained their offspring, reared them in common-garden conditions until adulthood and then tested them in similar social learning and shoaling tests to examine the heritability of these traits. Again we found evidence for the existence of a genetic component in shoaling behaviour, expressed as differences between sibling groups, but not in the subjects’ propensity to socially learn. In Chapter 3, we describe our first developmental approach, in which we directly manipulated the perceived value of social information during early life and examined if this influenced our subjects’ social learning propensities later on. We reared fry in the presence of adults demonstrating which of two food delivery locations contained food, with adults demonstrating the opposite location of food delivery, and without any adults. Only subjects exposed to demonstrators that led them to food in early life reliably copied demonstrator choices in a social learning test later in life. These results provide novel evidence that the usefulness of social cues to foraging locations during early life can drive social learning propensities in similar contexts later on. Moreover, social learning was not detected in our first tests immediately after the end of our developmental manipulations (day 45) but only in our second tests after a period of rearing in common-garden conditions (day 90), suggesting that social learning propensities develop over time or are expressed under specific circumstances. We continued with another developmental study examining the effects of early life predation risk and housing density on various behavioural traits such as boldness, exploration and grouping tendency (presented in Chapter 4). We tested the subjects at two time points, one shortly after the end of experimental treatments (day 50) and one after a period of common-garden conditions to establish if the observed influences were long-lasting (day 80). We found significant differences between sexes in all standard tests at both testing dates. Males were bolder and more exploratory; compared to females they spent more time shoaling and interacting with a group of stimulus fish but were more likely to leave the shoal to approach and enter a novel feeder. We also saw significant treatment effects in some of the behavioural measures but these were often confined within certain subgroups, indicating the existence of complex interactions between the analysed factors. Shortly after the second series of behavioural tests (day 85), we assessed the propensity of these fish to use (and retain) social information in a two-part shoal choice test within a potentially dangerous novel environment, the results of which are reported in Chapter 5. We found that predator exposed fish, and particularly male individuals, were more adept at using a social cue – shoal cohesion – to make shoaling decisions. These fish showed a preference for a loose shoal over a tight shoal (which in nature would typically indicate the presence of nearby potential threats). Predator exposed fish appeared to also retain this information after a short time interval and made similar choices regarding tank locations in the second part of the test when the shoals were absent. Overall, we found evidence for consistency and heritability in grouping behaviour, but although grouping tendencies were (to some extent) correlated with social learning propensities, we found no evidence for consistency and heritability in social learning. Further work is needed to examine if this was driven by the subjects’ poor performance on the social learning tasks or if it reflects a higher degree of flexibility in utilization of social learning compared to grouping behaviour. Furthermore, we saw that early environmental conditions and experiences play a major role in shaping the behavioural phenotype of an individual. We found that both cues about the value of social information and context cues like predation risk and population density in early life, can influence an individual’s reliance on social information later in life. Moreover, as males and females differ significantly in their strategies to maximize fitness and survival, these early life cues can affect the behaviour of the two sexes in different ways.Το πρώιμο περιβάλλον (περιβάλλον ανάπτυξης) παίζει καθοριστικό ρόλο στη διαμόρφωση του μορφολογικού, φυσιολογκού και συμπεριφορικού φαινοτύπου των ζώων, ενώ οι συνθηκες που επικρατούν κατά την ανάπτυξη, μπορούν δυνητικά να προετοιμάσουν έναν οργανισμό για το περιβάλλον που πρόκειται να αντιμετωπίσει όταν ενηλικιωθεί. Στην εν λόγω διατριβή, χρησιμοποίησα το γκάπι του Τρινιντάντ (Poecilia reticulata), ένα μικρό τροπικό ψάρι που αποτελεί οργανισμό-μοντέλο στην εξελικτική και συμπεριφορική οικολογία, για να μελετήσω την επίδραση του πρώιμου περιβάλλοντος στην συμπεριφορά, δίνοντας έμφαση στην κοινωνική συμπεριφορά (κοπάδιασμα και κοινωνική μάθηση). Το 1ο κεφάλαιο είναι εισαγωγικό και γίνεται συζήτηση των κυριότερων εννοιών που θα αναλυθούν στα επόμενα κεφάλαια, παραθέτωντας τη σχετική διαθέσιμη βιβλιογραφία. Συγκεκριμένα περιγράφω την κοινωνική συμπεριφορά, το πρώιμο πριβάλλον και η φαινοτυπική πλαστικότητα, καθώς και τα βασικά χαρακτηριστικά του σύστηματος μελέτης (γκάπι). Επίσης ανφέρονται οι στόχοι και η βασική δομή της διατριβής. Στο 2ο κεφάλαιο, με τη διενέργεια διαδοχικών πειραμάτων σε τακτά χρονικά διαστήματα εξετάστηκε αν συμπεριφορές όπως το κοπάδιασμα και η κοινωνική μάθηση παραμένουν σταθερές στο χρόνο (individual consistency). Έπειτα, μετά από αναπαραγωγή των ατόμων και εκτροφή των απογόνων τους, μελετήθηκε αν τα στοιχεία αυτά είναι κληρονομήσιμα (heritability). Στο 3ο κεφάλαιο, μελετήθηκε η επίδραση της ηλικίας και του πρώιμου κοινωνικού περιβάλλοντος στην κοινωνική μάθηση των ψαριών αυτών. Πραγματοποιήθηκε εκτροφή ψαριών σε διαφορετικές κοινωνικές συνθήκες (παρουσία/απουσία ενηλίκων ψαριών που παρείχαν πληροφορίες σχετικά με την τοποθεσία της τροφής) και έπειτα μελετήθηκε αν τα ψάρια αυτά χρησιμοποιούσαν κοινωνική μάθηση για να βρουν τροφή με ένα σύντομο συμπεριφορικό τεστ. Το τεστ αυτό πραγματοποιήθηκε δύο φορές, μια αμέσως μετά το τέλος της εκτροφής και μια αργότερα, μετά από μια περίοδο κανονικών συνθηκών, ώστε να εξεταστεί αν η ηλικία παίζει ρόλο στην ικανότητα κοινωνικής μάθησης. Στο 4ο και 5ο κεφάλαιο εξετάστηκε η επίδραση της παρουσίας θηρευτών και της πυκνότητας του πληθυσμού σε μια σειρά συμπεριφορικών χαρακτηριστικών των γκαπι. Στα πειράματα αυτά, έγινε προσομοίωση του καθεστώτος υψηλής ή χαμηλής θήρευσης που τα ψάρια αυτά συναντούν στη φύση, με τη χρήση χημικών αλλά και οπτικών ερεθισμάτων καιτά την εκτροφή. Ταυτόχρονα, η εκτροφή έγινε σε δυο συνθήκες πυκνότητας ψαριών, υψηλή και χαμηλή. Στη συνέχεια, εξετάστηκαν στοιχεία της συμπεριφοράς τους όπως τολμηρότητα (boldness), τάση εξερεύνησης, κοπάδιασμα, αποφυγή θηρευτών και κοινωνική μάθηση. Τέλος, στο 6ο κεφάλαιο, γίνεται ανακεφαλαίωση των σημαντικότερων ευρημάτων της διατριβής και συζήτησή τους ως προς την υπάρχουσα βιβλιογραφία. Ακόμη, περιγράφονται οι σημαντικότερες θεωρητικές και πρακτικές εφαρμογές των αποτελεσμάτων καθώς και πιθανές μελλοντικές κατευθύνσεις για περαιτέρω έρευνα.De snelle uitwisseling van informatie is een van de belangrijkste voordelen van het leven in een groep. Sociaal leren – het leren van anderen – biedt een snelle en voordelige manier om informatie over de lokale omgeving te verzamelen en is een strategie om gedrag aan te passen in uiteenlopende omstandigheden. Daarentegen kan sociale informatie ook onbetrouwbaar zijn of achterhaald worden in een snel veranderende omgeving. Dus, afhankelijk van bijbehorende kosten en baten, kan van flexibiliteit in het gebruik van sociaal leren verwacht worden dat het voordelig is in de meeste situaties. De vroege omgeving speelt een belangrijke rol in het vormen van het morfologische, fysiologische of gedragsmatige fenotype van een dier. De omstandigheden en ervaringen gedurende het vroege leven kunnen mogelijkerwijs een zich ontwikkelend individu voorbereiden (of programmeren) op de omgeving die het zal tegenkomen als volwassene. In deze thesis hebben we onderzocht of sociale gedragingen, zoals groepsgedrag en social leren, beοnvloed kunnen zijn door omstandigheden in het vroege leven en in welke mate. Hiervoor namen we twee stammen van de guppy Poecilia reticulata (gedomesticeerde en van wilde origine), een populair modelsysteem in gedragsen evolutionaire ecologie waarvan het sociaal gedrag goed beschreven is. In Hoofdstuk 2 presenteren we de studie waarin we onderzochten of neigingen tot schoolgedrag en sociaal gedrag consistent waren en of het erfelijke eigenschappen zijn. Ten eerste onderzochten we de individuen in vergelijkbare testen voor sociaal leren en schoolgedrag om de individuele consistentie in hun prestaties na te gaan. We vonden bewijs voor de consistentie van het schoolgedrag van de mannelijke guppy’s maar niet voor hun neigingen tot sociaal leren. We vonden geen bewijs voor individuele consistentie bij de vrouwelijke vissen. Vervolgens hebben we mannetjes en vrouwtjes willekeurig in paren ingedeeld, en hun nakomelingen opgekweekt tot volwassenheid in standaard omstandigheden. Daarna werden de nakomelingen getest op vergelijkbare sociaal leren en schoolgedrag testen om de erfelijkheid van deze eigenschappen te onderzoeken. Opnieuw vonden we bewijs voor het bestaan van een genetische component in schoolgedrag - er bestonden verschillen tussen groepen broers en zussen - maar niet in de neigingen van de guppy’s voor sociaal leren. In Hoofdstuk 3 beschrijven we de eerste ontwikkelingsaanpak, waarin we de waargenomen waarde van sociale informatie manipuleerden gedurende het vroege leven en onderzochten of dit in een later stadium de neigingen voor social leren beοnvloedde. We kweekten jonge vissen op in drie verschillende condities. In de eerste waren volwassen guppy’s aanwezig, die demonstreerden welke van twee voedsellocaties daadwerkelijk voedsel bevatte. In de tweede conditie toonden de volwassen vissen juist de tegenovergestelde locatie waar geen voedsel aanwezig was. In de laatste conditie waren er geen volwassen guppy’s aanwezig. Alleen guppy’s die opgroeiden met volwassen vissen die de correcte voedsellocatie toonden, kopieerden op betrouwbare wijze de keuzes van de demonstrerende vissen in een sociaal leren test in een latere situatie. Deze resultaten bieden nieuw bewijs dat het nut van sociale aanwijzingen naar foerageerlocaties gedurende het vroege leven kunnen leiden tot een vergrote neiging tot sociaal leren in vergelijkbare contexten op latere momenten. Bovendien werd sociaal leren niet gedetecteerd in onze eerste tests direct na het einde van de ontwikkelingsmanipulaties (dag 45) maar alleen in onze tweede tests na een periode van kweek in standard omstandigheden (dag 90), wat suggereert dat neigingen tot sociaal leren zich na verloop van tijd ontwikkelen of worden uitgedrukt onder specifieke omstandigheden. We vervolgden met een andere ontwikkelingsstudie waarin we de effecten van predatierisico en populatiedichtheid in het vroege leven op verschillende gedragskenmerken zoals neigingen tot vrijmoedigheid, exploratie en scholingsgedrag (gepresenteerd in Hoofdstuk 4). We testten de guppy’s op twee tijdpunten, ιιn kort na het einde van de experimentele behandeling (dag 50) en ιιn na een periode van standaard omstandigheden (dag 80) om vast te stellen of de geobserveerde invloeden langdurig waren. We vonden significante verschillen tussen de geslachten in alle standaard testen op beide testmomenten. Mannetjes waren vrijmoediger en exploreerden meer; vergeleken met vrouwtjes spendeerden zij meer tijd in scholingsgedrag en interacteerden meer met een groep stimulus-vissen, maar maar ook verlieten zij de school vaker om een nieuwe voedsellocatie te benaderen en binnen te gaan. We zagen ook significante behandelingseffecten in sommige gedragsmetingen, maar deze waren vaak beperkt tot bepaalde subgroepen, wat wijst op het bestaan van complexe interacties tussen de geanalyseerde factoren. Kort na de tweede reeks gedragstesten (dag 85), onderzochten we de neiging van deze vissen om sociale informatie te gebruiken (en te behouden) in een tweedelige schoolkeuze test binnen een potentieel gevaarlijke nieuwe omgeving, de resultaten hiervan worden gerapporteerd in Hoofdstuk 5. We vonden dat aan roofdieren blootgestelde vissen, en in het bijzonder mannelijke individuen, meer bedreven waren in het gebruik van sociale signalen – schoolcohesie - bij het maken van beslissingen in scholingsgedrag. Deze vissen toonden een voorkeur voor een losse school boven een dichte school (in de natuur zou dit doorgaans wijzen op de aanwezigheid van nabijgelegen potentiλle bedreigingen). Aan roofdieren blootgestelde vissen leken deze informatie ook te behouden na een korte tijdsperiode en maakten vergelijkbare keuzes over aquarium locaties in het tweede deel van de test, toen de scholen afwezig waren. Over het geheel genomen hebben we bewijs gevonden voor consistentie en erfelijkheid van scholingsgedrag, maar hoewel de neiging tot groeperen (tot op zekere hoogte) gecorreleerd waren met neigingen tot sociaal leren vonden we geen bewijs voor de consistentie en erfelijkheid van sociaal leren. Verder onderzoek is nodig om na te gaan of dit werd veroorzaakt door de slechte prestaties van de guppy’s in de testen voor sociaal leren, of dat het meer flexibiliteit in de benutting van sociaal leren vergeleken met scholingsgedrag weerspiegelt. Verder zagen we dat de vroege omgevingsomstandigheden en ervaringen een belangrijke rol spelen in het gedragsfenotype van een individu. We vonden dat een individu’s afhankelijkheid van sociale informatie op latere leeftijd afhangt van zowel signalen over de waarde van sociale informatie als contextuele signalen, zoals predatierisico en populatiedichtheid in het vroege leven. Aangezien de mannetjes en vrouwtjes significant verschillen in hun strategieλn om fitness en overleving te maximaliseren, kunnen deze signalen in het vroege leven het gedrag van de twee geslachten op verschillende manieren beοnvloeden

Data from: Age and early social environment influence guppy social learning propensities

Social learning, learning from others, allows animals to quickly and adaptively adjust to changing environments, but only if social learning provides reliable, useful information in that environment. Early life conditions provide a potential cue to the reliability of social information later in life. Here, we addressed whether direct early life experience of the utility of social learning influences later social learning propensities. We reared guppy, Poecilia reticulata, fry for 45 days in three different social conditions which involved the presence of adult demonstrators providing cues about feeding locations in the tanks (‘follow adults’ and ‘avoid adults’ treatments), or their absence (‘no adults’ treatment). In the ‘follow adults’ treatment, juveniles that swam in the same direction as the adult demonstrators found food, whereas in the ‘avoid adults’ treatment, subjects that swam in the opposite direction to the demonstrators found food. We then tested the fish with a social learning task, to examine whether prior experience had influenced the social learning tendencies of the juveniles. After another 45 days of rearing under common-garden conditions with no adult fish present in the tanks, subjects were retested with the same social learning task, to investigate whether early experiences had effects persisting into adulthood. After 45 days of rearing we found no evidence for social learning in any of the experimental groups. However, after 90 days of rearing, we found evidence of social learning, but only in the ‘follow adults’ treatment. These results suggest that social learning propensities may develop over life, and that prior exposure to conspecifics providing useful foraging information during early life can shape the degree of reliance on social learning in adulthood

Dataset

Please refer to ReadMe file

In search of the unexpected: the first finding of an islandic population of the noble crayfish

This contribution presents the first record of the noble crayfish Astacus astacus (Linnaeus, 1758) in Euboea (Evia) Island, Greece. The crayfish was found during a fish monitoring expedition in the upper Mesapios River, in a reach that maintains flow throughout the year, while most of the river length desiccates completely during the dry season. The finding of A. astacus in an intermittent river of Euboea Island expands the species geographical range and calls for immediate conservation actions to protect its habitat and preserve this vulnerable population

Data from: Wild and laboratory exposure to cues of predation risk increases relative brain mass in male guppies

There is considerable diversity in brain size within and among species, and substantial dispute over the causes, consequences and importance of this variation. Comparative and developmental studies are essential in addressing this controversy. Predation pressure has been proposed as a major force shaping brain, behaviour and life history. The Trinidadian guppy, Poecilia reticulata, shows dramatic variation in predation pressure across populations. We compared the brain mass of guppies from high and low predation populations collected in the wild. Male but not female guppies exposed to high predation possessed heavier brains for their body size compared to fish from low predation populations. The brain is a plastic organ, so it is possible that the population differences we observed were partly due to developmental responses rather than evolved differences. In a follow‐up study, we raised guppies under cues of predation risk or in a control condition. Male guppies exposed to predator cues early in life had heavier brains relative to their body size than control males, while females showed no significant effect of treatment. Collectively our results suggest that male guppies exposed to predation invest more in neural tissue, and that these differences are at least partly driven by plastic responses

Data from: Developmental plasticity of the stress response in female but not male guppies

To survive, animals must respond appropriately to stress. Stress responses are costly, so early-life experiences with potential stressors could adaptively tailor adult stress responses to local conditions. However, how multiple stressors influence the development of the stress response remains unclear, as is the role of sex. Trinidadian guppies (Poecilia reticulata) are small fish with extensive life history differences between the sexes and population variation in predation pressure and social density. We investigated how sex and early-life experience influence hormonal stress responses by manipulating conspecific density and perceived predation risk during development. In adults, we sampled cortisol twice to measure initial release and change over time in response to a recurring stressor. The sexes differed considerably in their physiological stress response. Males released more cortisol for their body mass than females and did not reduce cortisol release over time. By contrast, all females, except those reared at high density with predation cues, reduced cortisol release over time. Cortisol responses of males were less dynamic in response to current circumstances and early-life experiences than females, consistent with life history differences between the sexes. Our study underscores the importance of early-life experiences, interacting ecological factors, and sex differences in the organization of the stress response