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Life history shifts in an exploited African fish following invasion by a castrating parasite

Citation

Gabagambi, Nestory Peter et al. (2020), Life history shifts in an exploited African fish following invasion by a castrating parasite, Dryad, Dataset, https://doi.org/10.5061/dryad.p2ngf1vp3

Abstract

Evolutionary theory predicts that infection by a parasite that reduces future host survival or fecundity should select for increased investment in current reproduction. In this study we use the cestode Ligula intestinalis and its intermediate fish host Engraulicypris sardella in Wissman Bay, Lake Nyasa (Tanzania) as a model system. Using data about infection of E. sardella fish hosts by L. intestinalis collected for a period of 10 years, we explored whether parasite infection affects the fecundity of the fish host E. sardella, and whether host reproductive investment has increased at the expense of somatic growth. We found that L. intestinalis had a strong negative effect on the fecundity of its intermediate fish host. For the non-infected fish we observed an increase in relative gonadal weight at maturity over the study period, while size at maturity decreased. These findings suggest that the life history of E. sardella has been shifting towards earlier reproduction. Further studies are warranted to assess whether these changes reflect plastic or evolutionary responses. We also discuss the interaction between parasite and fishery-mediated selection as a possible explanation for the decline of E. sardella stock in the lake.

Usage Notes

Data_usipa_all_wissman.txt (used for analyses and figures 2-3 & A2)

Month2 – continuous month count (1=January 2005)
Day – calendar day
Month – calendar month
Year – calendar year
Season – dry/wet season
Length_usipa – body length in mm
Weight_usipa – body weight in g
Sex_usipa - sex
Maturity_stage – maturity stage
Maturity_status – 0: stages I-III, 1: stages IV-VII
Postmaturity_status – 0: stages I-IV, 1: stages V-VII
Ligula_count – number of individual parasites found
Infection – 0: non-infected, 1: infected
Weight_gonad – wet weight of gonads
Number_eggs – number of eggs counted in gonads
Somatic_weight – calculated as (total weight – weight of gonads)
GSI – gonadosomatic index in %
Condition_factor – Fulton index
Repro_status – 0: pre-spawn, 1: ready to spawn or post-spawn

Yearlydata.txt (used for analysis and figures 3 & A3)

Year – calendar year
Inf_peakfec – number of infected fish at stages IV-V
Total_peakfec – total number of fish at stages IV-V
Prev_peakfec – prevalence at stages IV-V
Inf_mature- number of infected fish at stages IV-VII
Total_mature – total number of fish at stages IV-VII
Prev_mature – prevalence at stages IV-VII
Inf_immat - number of infected fish at stages I-III
Total_immat - total number of fish at stages I-III
Prev_immat – prevalence at stages I-III
Inf_all – number of infected fish, all stages
Total – total number of fish
Prev_all – prevalence, all stages
Rel-abund_immat – relative abundance of stages I-III
Rel-abund_peakfec – relative abundance of stages IV-V
Rel-abund_mat – relative abundance of stages IV-VII
LM50_all – LM50 for all fish
LM50_inf – LM50 for infected fish only
LM50_uninf – LM50 for uninfected fish only
Number_of_fishermen – number of fishermen registered
Fishing_pressure – number of fishermen per tonne landed
Landed_per_fisherman –number of tonnes landed per fisherman

Funding

Norwegian State Education Loan Fund, Award: 2872580

Norwegian State Education Loan Fund, Award: 2872580