DOI: 10.5061/dryad.vmcvdnd47
title: Data from: Parasites alter interaction patterns in fish social networks

description: Social networks influence the spread of parasites through populations.
 Although we know how parasites are transmitted as a product of social
 interactions, we have a limited understanding of how social networks are
 affected by parasites over time. Host–parasite interactions and the
 networks they form, are typically examined as static networks, and while
 topological descriptions at a specific time point are useful, both
 behaviour and the infection process are dynamic. By monitoring replicate
 populations of Trinidadian guppies (Poecilia reticulata) daily before and
 during infection with the ectoparasite Gyrodactylus turnbulli, we show how
 parasitism drives social network dynamics. Specifically, infected
 individuals increased their connections in networks affected by
 parasitism. In contrast, uninfected control shoals showed no change in
 network metrics. The structure of subnetworks (motifs) and networks,
 however, did not change in response to infection status. These findings
 provide further evidence of reciprocal host behaviour–parasite feedback
 mechanisms, and highlight that infected fish alter their interactions in
 order to ‘off-load’ their parasites. Understanding how these reciprocal
 interactions affect the structure and function of natural systems, as well
 as understanding how these interactions may alter with future
 environmental change, are key areas of future research.
description: <strong>Host-parasite system</strong>
 Trinidadian guppies (<em>Poecilia reticulata</em>)
 were laboratory-reared descendants of wild-caught stock from the Lower
 Aripo River, Trinidad, in 2012. Fish were initially housed at the
 University of Exeter, before transfer to Cardiff University in 2014 to be
 maintained in 70 L dechlorinated water tanks under standard conditions of
 24 ± 0.5°C on a 12 h light: 12 h dark photoperiod (Lights on 07:00–19:00).
 Fish were fed daily on Aquarian® Tropical fish flakes, subsidised with
 freshly hatched <em>Artemia salina</em> and adult
 <em>Daphnia magna</em>. Aquaria were checked weekly for fry,
 which were transferred to rearing tanks from which female fish were
 isolated at 8-12 weeks. Only female guppies (n=120) were used due to their
 greater propensity to shoal than males (Griffiths & Magurran,
 1998), but also to avoid the confounding effects of male courtship
 behaviour and sexual interactions on parasite transmission and social
 network structure. For experimental infections, we used
 the isogenic <em>Gt3</em> strain of <em>Gyrodactylus
 turnbulli</em>, which originated from a single worm isolated from an
 ornamental guppy in 1997. This ectoparasite population has since been
 maintained in culture as described by Stewart et al. (2017). The
 monogenean worm is a common ectoparasite of guppies in both wild and
 ornamental stocks, and has a range of physiological and behavioural
 impacts (Croft et al., 2011; Stewart et al., 2017; Arapi et al., 2024). It
 is directly transmitted, transferring from host to host when the fish
 contact one another and has a short generation time, giving birth to live
 (already pregnant) young that attach to the fish alongside the parent worm
 (Bakke et al., 2007). To experimentally infect a fish, an infected (donor)
 fish from the culture was sacrificed via cranial destruction, and the
 caudal fin brought into close contact with a naïve (recipient) guppy,
 which had been temporarily anesthetised with 0.02% tricaine
 methansulfonate (MS-222). The transfer of parasites was observed under a
 dissecting microscope with fibre-optic illumination, following the
 standard methods of King & Cable (2007). Control fish (i.e., sham
 infected) were handled and exposed to anaesthetic in the same manner as
 the experimental fish but without exposure to parasitic infection.
 Parasite infections were monitored non-destructively throughout the
 experiment by again briefly anaesthetising each fish in a shoal (including
 the control shoals) and counting the number of external worms on the
 surface of the fish using a dissecting microscope.
   <strong>Experimental
 setup</strong> Experimental trials took place in
 a 70 L tank of dechlorinated water, maintained under standard light and
 temperature conditions (see <em>Host-parasite system</em>). A
 2 cm layer of fine gravel substrate filled the base of the aquarium, which
 was lit from above using daylight mimicking strip lights (Sylvania T5
 F13W/54-765 G5 Luxline Standard Daylight bulb) diffused by white fabric.
 The chamber was surrounded on three sides with opaque white fabric to
 prevent external disturbances, with one side left open to allow for
 observations.  
 <strong>Behavioural experiments</strong>
 A total of 20 replicate shoals, each containing six sized-matched
 female <em>P. reticulata</em>, were monitored daily for 10
 days, with experimental infection occurring on day 5 in 15 randomly
 selected replicates, and a sham infection in the remaining five controls.
 Each fish was uniquely marked using visual implant elastomer (VIE),
 enabling individual fish identification during a trial. To do this, fish
 were briefly anaesthetised using 0.02% MS222, and VIE injected into the
 ventral or dorsal muscle tissue. This is a marking procedure extensively
 used in guppies (Croft et al., 2006, 2009; Hasenjager & Dugatkin,
 2017; Wilson et al., 2015) that does not appear to influence social
 behaviour (Croft et al., 2004). Fish standard length
 (SL; mm) was measured before each group was placed into a separate 5 L
 aquarium to form shoals over a 2-week familiarisation period (Griffiths
 & Magurran, 1997), before transferring to an experimental chamber
 to acclimate for 24 h. On day 5, all fish were
 temporarily isolated in individual 1 L pots and either the most or least
 connected shoal member (determined by assessing accumulated contact
 frequency data until day 5; see ‘<em>social network
 construction’</em>, below) was infected with exactly 30 <em>G.
 turnbulli</em> individuals. This procedure formed three experimental
 treatments: most connected infected (n = 7 shoals), least connected
 infected (n= 8 shoals), and uninfected controls (n = 5 shoals). The
 unbalanced experimental design arose through limited availability of
 mature female fish for the experiment. Despite uneven sample sizes, an
 adequate number of replicates ensured that robust statistical analysis
 comparing experimental treatments could be performed. Within each infected
 shoal, a single fish was experimentally infected and the remaining five
 fish in each shoal, as well as each fish in the control groups, were sham
 infected by anaesthetising and manipulating under the microscope, but
 without exposure to parasites. Fish were revived in 1 L dechlorinated
 water and returned to their shoal groups. Infection was confirmed on day
 6, and each fish was screened on consecutive days thereafter (days 7, 8, 9
 and 10) to quantify <em>G. turnbulli</em> intensity, following
 behavioural observations. At each time step control and experimental
 groups underwent the same experimental procedures; anaesthesia followed by
 handling.   <strong>Social
 network construction</strong> For each shoal,
 interactions were monitored on each day (1-10) for a 10 min period
 (between 9:00–12:00, 3 shoals per experiment). The frequency of
 interactions between individuals (the number of direct contact events;
 e.g., skin-skin contact including a bite or the brushing of fins,
 typically lasting &lt;1 sec) was recorded for all individuals, as well
 at the directionality of the interactions (i.e., which fish initiated the
 interaction). This resulted in a series of directed, weighted networks,
 where individuals are represented by nodes and interactions between
 individual fish by edges. Each behaviour recorded was directional such
 that we could record who approached whom giving us the ability to quantify
 the number of outgoing contacts from shoal mates (‘out degree’) and the
 number of incoming contacts (‘in degree’). Because multiple interactions
 can occur over time these edges, or interactions within the network were
 weighted; i.e., were a simple count of how many times they
 occurred.
description: # Data from: Parasites alter interaction patterns in fish social networks
 Dataset DOI: [10.5061/dryad.vmcvdnd47](10.5061/dryad.vmcvdnd47) ##
 Description of the data and file structure Behavioural experiments were
 conducted on 20 guppy shoals in a controlled aquarium environment to study
 social interactions and parasite transmission dynamics. Each shoal of six
 marked females was observed daily for 10 days, with 15 shoals receiving
 experimental parasite infections and 5 serving as controls. Fish
 interactions were recorded to build daily directed, weighted social
 networks, capturing in- and out-degrees, betweenness centrality, and
 transmission-relevant motifs. Infection intensity and network metrics were
 generated from these data to assess how social structure influences
 parasite spread. ### Files and variables #### File: ind_infect.csv
 **Description:** The infection data for individuals within the
 experimental systems. ##### Variables * shoal: The unique shoal identifier
 (categorical; alphabetic code) * fish_id: The unique identifier for the
 individual fish (categorical; alphabetic code) * time: The day the of the
 trial on which the measurements were recorded (integer; 1-10) *
 parasite_intensity: The number of *Gyrodactylus turnbulli* individuals
 recorded on an individual fish (integer; 0-182) #### File: ind_target.csv
 **Description:** Meta-data on the individuals that were the initial target
 for infections within the experimental setup (i.e., which fish were
 artificially infected). ##### Variables * shoal: The unique shoal
 identifier (categorical; alphabetic code) * target: The unique identifier
 for the individual fish that was the target for artificial infection
 (categorical; alphabetic code). "null" indicates that no fish
 were infected in the control systems. * infection: The target of
 infections status within the network on day (1-5) - least (the individual
 with the least connections), most (the individual with the most
 connections) or control (no individual was infected). Connections are
 defined as the accumulated contact frequency data until day 5.
 (categorical; least or most) #### File: social_nets.csv
 **Description:** The edgelists for the social interactions between
 individual fish recorded over the experiments. ##### Variables *
 shoal: The unique shoal identifier (categorical; alphabetic code) * time:
 The day the of the trial on which the measurements were recorded (integer;
 1-10) * lower: The lower individual in the interaction (i.e., the
 individual receiving the interaction) (categorical; alphabetic code) *
 upper: The upper individual in the interaction (i.e., the individual
 engaging in the interaction) (categorical; alphabetic code) * weight: The
 number of interactions between the two individuals (integer; 1-13) ##
 Code/software R software was used for analysis (version 4.4.1). A live,
 updated version of the code used for analyses can be found
 at [https://github.com/fmwindsor/social-parasites](https://github.com/fmwindsor/social-parasites).  ## Access information Other publicly accessible locations of the data: * [https://github.com/fmwindsor/social-parasites](https://github.com/fmwindsor/social-parasites) Data was derived from the following sources: * N/A