Palaemon macrodactylys and Gobiosoma parri behaviour set
; Bas, Claudia Cristina Otros responsables
Fecha
Publicador:
Consejo Nacional de Investigaciones Científicas y Técnicas
Fecha de depósito:
14/03/2023
Fecha de creación:
25/2/2021-26/6/2021
Clasificación temática
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Resumen
Behavioural traits play an important role in invasion success, yet little is known about how species behave when they arrive in a new environment. In this study we examined the behaviour of the invasive shrimp Palaemon macrodactylus after entering in a novel place with a single refuge during a 24 h solitary phase, and after the introduction of a conspecific or heterospecific (the native goby Gobiosoma parri), in the next 24 h (competition phase), comparing their responses as residents and as intruders. Time spent swimming, using the shelter and the frequency of interactions (withdrawing touches) were quantified. Shrimps entering to a new empty environment, swam most of the time in the first hours, while the use of shelter increased steadily. The use of shelter in shrimps was affected by sex and residency status. Females won the shelter to males, while residents won the shelter to intruders. In the interspecific competition, refuge was always won by gobies and shrimps showed no resistance. Obtaining shelter was not generated through aggressive behaviours, but rather a hierarchy established through some other type of interactions. We propose that both prolonged swimming, which could indicate exploratory behaviour, and a social organization without aggressive confrontations could be key to the initiation of an invasion in this species.
Métodos
Shrimps and gobies were collected with a hand net in Mar del Plata harbour. The experimental aquaria consisted of an opaque container (20 x 25 x 15 cm), filled with 3000 ml sea water. An opaque plastic half cylinder (2 cm diameter and 3.5 cm length) located at the centre of the aquarium floor was offered as refuge. A video camera was installed 50 cm above the aquaria to record the behaviour of the animals along the experiment. In each trial, residency status was established by placing one individual into the experimental aquarium 24 h alone (solitary phase), while it was recorded. By previous observations this is the period after which the time spent swimming and inside the refuge become stable in shrimps, and the same period was used for gobies. We considered as intruders the individuals coming into a space already occupied by a resident. The interactions between residents and intruders (the competition phase) were monitored for 24 h, so, each complete trial lasted 48 h. We performed 44 experimental trials (half of intraspecific pairs and the other half of heterospecific pairs) between February 25 and June 26, 2016. The trials of the different pairs were conducted randomly over time. From each trial recorded during 48 h, we analysed one-hour periods every four hours, starting at the first hour of each experiment. In this way, from each complete 48 hours trial we analysed 12 periods of one hour; the first six corresponding to the solitary phase on day 1 and the others to the competition phase on day 2. We observed three behaviours not involving interactions between individuals: swimming, when individuals were moving through the aquarium propelled by their pleopods, walking on the bottom, and standing still resting on the pereiopods at the bottom of the aquarium or inside the shelter. The only physical interaction consistently produced by shrimps was a contact in which one of the members of the pair touched the other with one cheliped. When the touched animal was another shrimp, it always moved away. We named this behaviour as withdrawing touch. From the stationary activities of shrimps, only the time spent inside the refuge was quantified. The introduction of at least 50% of the body into the shelter for at least 3 seconds was accounted as use of the shelter. Similarly, the only quantified motion activity was swimming, because walking activity was barely performed. All swimming episodes longer than 3 seconds were included. The time spent by animals standing still in the bottom was the complementary fraction of time swimming + time inside the refuge and was not analysed. Finally, the number of withdrawing touches produced by shrimps from all pairs were quantified. Only the time spent in the refuge was quantified for gobies, using the same criteria as with shrimps. Almost no interactions were performed between shrimps and gobies, so they were not analysed. All the videos were visually analysed by a single observer. The duration of each individual activity was timed with a manual stopwatch separately for each of the observation periods, for each member of the pair separately, repeating the video as many times as necessary. The number of touches produced by each shrimp was also counted.
To evaluate behaviour differences between shrimps entering a new environment with and without the presence of another individual (conspecific or native goby), the time spent in the shelter and the time spent swimming were compared with LME, with sex of shrimp, type of environment (empty, with male shrimp, with female shrimp or with goby) as fixed factor and period (1 to 6) as covariate. Individual nested to period was considered as a random factor.
To evaluate how the behaviour of residents changed according to the type of intruder, the time spent in the shelter and the time spent swimming were compared between resident shrimps in the competition phase, with LME, with sex of resident shrimp and type of intruder (male shrimp, female shrimp or goby) as fixed factor and period (1 to 6) as covariate. Individual nested to period was considered as a random factor.
The number of withdrawing touches produced by each shrimp in a pair was evaluated with LME for the sum of the six periods of the competition phase, due to the low number of touches produced in each period. Sex and residency status of touching shrimp, and sex of the displaced shrimp were considered as fixed factors. The pair was considered as random factor.
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