Sex identification and PIT‐tagging: tools and prospects for studying intersexual differences in freshwater fishes

Studies of predator-mediated selection on behaviour are critical for our understanding of the evolution and maintenance of behavioural diversity in natural populations. Consistent individual differences in prey behaviour, especially in the propensity to take risks (“boldness”), are widespread in the animal kingdom. Theory predicts that individual behavioural types differ in a cost-benefit trade-off where bolder individuals benefit from greater access to resources while paying higher predation-risk costs. However, explicitly linking predation events to individual behaviour under natural conditions is challenging and there is currently little data from the wild. We assayed individual behaviour and electronically tagged hundreds of fish (roach, Rutilus rutilus) before releasing them into their lake of origin, thereby exposing them to predation risk from avian apex predators (cormorants, Phalacrocorax carbo). Scanning for regurgitated tags at the cormorant roosting site provided data on individual predation events. We found that fish with higher boldness have a greater susceptibility to cormorant predation compared to relatively shy, risk-averse individuals. Our findings hereby provide unique and direct evidence of behavioural type-dependent predation vulnerability in the wild, i.e. that there is a predation cost to boldness, which is critical for our understanding of the evolution and maintenance of behavioural diversity in natural populations.

Section: Methodsmentioning

confidence: 88%

A predation cost to bold fish in the wild

Hulthén

Chapman

Nilsson

et al. 2017

“…After fish anesthetization, a 4–5 mm vertical incision was made 3 cm posterior to the pelvic fin, and a 32 mm PIT tag for asp (Oregon RFID, half-duplex, diameter 3.65 mm, weight 0.8 g, ISO 11784/11785 compatible) or a 23 mm PIT tag for bleak (Oregon RFID, half-duplex, diameter 3.65 mm, weight 0.6 g, ISO 11784/11785 compatible) was inserted into the body cavity. No sutures were used to close the incision according to cyprinid tagging methodology 28 , 29 . The tagged individuals were released immediately after recovery from anaesthesia.…”

Section: Methodsmentioning

confidence: 99%

Nocturnal spawning as a way to avoid egg exposure to diurnal predators

Šmejkal

Souza

Blabolil

et al. 2018

Animals that do not provide parental care have to secure the survival of their offspring by ensuring a safe reproductive environment or smart timing tactics. Nocturnal spawning behaviour of many fish species is an example of the latter behaviour in the animal kingdom and is hypothesized to provide a survival advantage to the eggs spawned during the night. In order to test the efficiency of the smart timing tactics in a freshwater fish, a study was carried out of the interaction of the rheophilic spawner (asp Leuciscus aspius) and the predator of its drifting eggs (bleak Alburnus alburnus) using passive telemetry. According to a model based on acquired data, asp laid 63% of its eggs at night, while vision-oriented bleak was present in 92% of the time during the day. This study gives support to the predator avoidance hypothesis, which expects animals to reproduce in a period when the probability of offspring predation is at its lowest.

“…After removing 3–4 scales, a 4–5 mm vertical incision was made 3 cm posterior to the pelvic fin, and a PIT tag (Oregon RFID, half-duplex, length 32 mm, diameter 3.65 mm, weight 0.8 g, ISO 11784/11785 compatible) was inserted into the body cavity. No sutures were used to close the incision, according to a previously described cyprinid tagging methodology 48, 49 . The tagged individuals were released immediately after recovery from anaesthesia.…”

Section: Methodsmentioning

confidence: 99%

Seasonal and daily protandry in a cyprinid fish

Šmejkal

Ricard

Vejřík

et al. 2017

In polygynandrous mating systems, in which females limit reproductive success, males can increase their success by investing in courtship. Earlier arrival at the spawning ground compared to when females arrive may increase their opportunities in competitive mating systems. In this study, we used passive telemetry to test whether a male minnow known as the asp, Leuciscus aspius, times its arrival at spawning grounds relative to the arrival of females. Males arrived in a model stream approximately five days earlier than females on average and left four to five days later than females over two years. Both sexes performed a daily migration between a staging ground (standing water, low energy costs) and the fluvial spawning ground (high energy costs). Fish abundance peaked twice a day, with a major peak at sunset and a minor peak at sunrise and with the evening peak abundance for males occurring 1 hour 40 minutes earlier than that of females. The number of females on the spawning ground never exceeded the number of males. While the degree of protandry is hypothesized to be influenced by the operational sex ratio (ranging from 0.5 to 1 in our study), our data did not support this theory.