An analysis of the relationships between skin and eye colouration, reproductive strategy and habitat for Swedish marine and brackish teleosts Tom Audhav Ämneslärarprogrammet Examensarbete: 15 hp Kurs: LGBI1G Självständigt arbete (examensarbete) 1 för gymnasielärare i biologi Institution: Institutionen för biologi och miljövetenskap Göteborgs universitet Nivå: Grundnivå Termin/år: HT/2014 Handledare: Docent Helen Nilsson Sköld Institutionen för biologi och miljövetenskap, Göteborgs universitet Examinator: Susanne Pihl Baden Institutionen för biologi och miljövetenskap, Göteborgs universitet Kod: HT14-3130-001-LGBI1G Nyckelord: Coloration, Reproductive strategy, Teleost, mate choice, Sexual selection Abstract We live in a time of rapid and easy sharing of data. Online databases allow scientist from all over the world to instantly share their results with the whole scientific community. One such database is fishBase (Froese & Pauly, Editors 2014), where people from all over the world collect pictures and basic data on all the world's fish species. The amount of readily available data allows for exploratory and comparative studies to be conducted without individual data collection but by putting the pre-existing data under the filter of new questions. This study uses fishBase and the Swedish Nationalnyckeln, (Kullander, Nyman, Jilg & Delling, 2012) to explore the relationship of conspicuous and cryptic colouration of skin and eyes to reproduction strategy, structural and colour complexity of the habitat and depth preference in Swedish marine and brackish teleosts. There have been many studies in the past exploring the function of contrasting skin colouration, and have found it to, be a faithful conveyor of fitness. This is however, to our knowledge, the first exploratory study on a species level, and also the first to consider eye colouration as a possible important variable. Each variable was compared for significance and impact on the colour traits using the method of logistic regression. The study found a positive correlation between species who mate in pairs of one male and one female (here after paired coupling reproduction), in contrast to the for fish more common group mating and contrasting skin colouration as well as contrasting eye colouration, both when considered separately and when considered together. Contrasting eye colouration was almost as good a predictor for paired coupled mating as was contrasting skin, and species with paired coupling reproduction, and at least one of these traits where found in very separate evolutionary groups. No clear link between conspicuous traits and habitat structure was established even though reproduction strategy and habitat structure were shown to correlate to an extent. Even more unexpected was the apparent lack of correlation between visually conspicuous traits and depth preference. We suggest that paired coupling reproduction considerably raises the selection pressure for faithfully signaling high fitness, that this can be done by eye as well as skin colouration and that this has caused the same relationship between reproduction strategy and visually conspicuous traits to occur separately several in different evolutionary groups over the course of history. Sammanfattning Det har aldrig varit lättare eller snabbare för människor att dela med sig av data till varandra, internetbaserade databaser tillåter forskare att dela med sig av sin datainsamling och sina forskningsresultat med hela resten av världen på ett sätt som för några årtionden sedan hade varit otänkbart. En sådan databas är fishBase (Froese & Pauly, Editors 2014), där forskare över hela världen samlar bilder och grundläggande data om alla världens fiskarter. Mängden tillgänglig data gör det möjligt att utföra undersökande och jämnförande studier utan att samla in egen data utan istället genom att titta på datan med nya frågeställningar. Denna studie använder sig av fishBase och Nationalnyckeln för att undersöka visuellt iögonfallande fysiska drag så som hudfärg som kontrasterar med habitatets färger och ögonfärg som kontrasterar med hudfärgen hos svenska marina och bracktvattenfiskar och dessa drags möjliga förhållande med djuppreferens, habitatstruktur och reproduktionsstrategi. Variablerna i varje kategori blev tilldelade numeriska värden och jämfördes med varandra genom den statistiska metoden logistisk reduktion för att få reda på de olika variablernas signifikans och deras eventuella påverkan på de visuella dragen. Studien fann en tydlig positiv koppling mellan visuellt iögonfallande drag och reproduktionsstrategin parvis förökning, både när ögonfärg och hudfärg undersöktes separat och när de slogs samman till en kategori. Ingen tydlig länk hittades mellan visuellt iögonfallande egenskaper och habitatets strukturella komplexitet trots att reproduktionsstrategi ser ut att till en viss grad korrelera med densamma och kanske ännu mer oväntat så hittdes ingen länk mellan djuppreferens och visuellt iögonfallande egenskaper. Sambandet mellan vissuelt iögonfallande egenskaper och reproduktionsstrategi hittades i ett flertal evolutionära grupper, många av vissa även inehåller kryptiska arter, vi föreslår därför att ett starkt selektionstryck för kontrasterande drag har fått dessa att uppstå flera gånger under evolutionens gång. Table of Contents Abstract ..................................................................................................................................... 3 Sammanfattning ....................................................................................................................... 3 Introduction .............................................................................................................................. 5 Teleostei ............................................................................................................................. 5 Colouration ........................................................................................................................ 5 Habitat ............................................................................................................................... 5 Reproduction ..................................................................................................................... 5 Visibility ............................................................................................................................ 7 Background ............................................................................................................................... 7 Aim of Study ............................................................................................................................. 7 Glossary ............................................................................................................................. 7 Material and methods .............................................................................................................. 8 Image analysis ................................................................................................................... 8 Data collection and categorization .................................................................................... 8 Statistics ............................................................................................................................. 8 Results ....................................................................................................................................... 9 Skin and eye colouration in relation to reproductive strategy ........................................... 9 Crypsis or contrasting colouration of species with paired coupling in relation to evolution 11 Reproduction strategy in relation to colouration and habitat .......................................... 14 Discussion ................................................................................................................................ 14 Pedagogisk koppling, examensarbete i biologi .................................................................... 17 Acknowledgment .................................................................................................................... 17 Sources ..................................................................................................................................... 18 Apendix ................................................................................................................................... 20 Complete data set ............................................................................................................. 20 Statistics ........................................................................................................................... 23 Contrasting by evolutionary order ................................................................................... 25 Introduction Teleostei Teleostei is a large evolutionary group containing the majority of the non extinct species of fish. What distinguishes the group is rayed fins, a skeleton made up of proper calcified bone, a spine that does not continue out to the tail fin and movable jaws. It arose around the early Permian era and has diversified in to more than 440 families, from eels and congers to salmons, perches and flatfish (see illustration 1). Teleosts are found all over the world from the tropics to the icy waters of the poles, from the shallow water near the coasts to depths unexplored by man and in sweet and salt water alike. They range in size from less than