Ocean warming favours a northern Argyrosomus species over its southern congener, whereas preliminary metabolic evidence suggests that hybridization may promote their adaptation

Abstract Anthropogenic-induced climate change is having profound impacts on aquatic ecosystems, and the resilience of fish populations will be determined by their response to these impacts. The northern Namibian coast is an ocean warming hotspot, with temperatures rising faster than the global average. The rapid warming in Namibia has had considerable impacts on marine fauna, such as the southern extension of the distribution of Argyrosomus coronus from southern Angola into northern Namibian waters, where it now overlaps and hybridizes with the closely related Namibian species, A. inodorus. Understanding how these species (and their hybrids) perform at current and future temperatures is vital to optimize adaptive management for Argyrosomus species. Intermittent flow-through respirometry was used to quantify standard and maximum metabolic rates for Argyrosomus individuals across a range of temperatures. The modelled aerobic scope (AS) of A. inodorus was notably higher at cooler temperatures (12, 15, 18 and 21°C) compared with that of A. coronus, whereas the AS was similar at 24°C. Although only five hybrids were detected and three modelled, their AS was in the upper bounds of the models at 15, 18 and 24°C. These findings suggest that the warming conditions in northern Namibia may increasingly favour A. coronus and promote the poleward movement of the leading edge of their southern distribution. In contrast, the poor aerobic performance of both species at cold temperatures (12°C) suggests that the cold water associated with the permanent Lüderitz Upwelling Cell in the south may constrain both species to central Namibia. This is most concerning for A. inodorus because it may be subjected to a considerable coastal squeeze.

Nucleotide (π) and haplotype (h) diversity were higher for A. coronus in comparison with A. inodorus (π = 0.0040, h = 0.730; vs π = 0.0018, h = 0.370, respectively).Summary indices of variability for the A. inodorus and A. coronus groups are reported in Table S2.The multilocus FST between both groups was 0.24.Microsatellite-derived genotype proportions conformed to Hardy-Weinberg equilibrium for each species group vs. locus combination, with the exception of UBA853 for the A.

Parallel
We used a single blank at the end of the trial and assumed that represented background respiration throughout the trial 32 Level of background respiration (e.g. as a percentage of SMR) <1%

33
Method and frequency of system cleaning (e.g.system bleached between each trial, UV lamp) The system was completely flushed, bleached and replaced with fresh seawater between each trial

STANDARD OR ROUTINE METABOLIC RATE 34
Acclimation time after transfer to chamber, or alternatively, time to reach beginning of metabolic rate measurements after introduction to chamber 12 hours 35 Time period, within a trial, over which oxygen uptake was measured (e.g.number of hours) 22 hours 51 How oxygen uptake rates were calculated (software or script, equation, units, etc.) Equation 52Confirm that volume (mass) of animal was subtracted from respirometer volume when calculating oxygen uptake rates Confirmed 53 State whether analyses accounted for variation in body mass and describe any allometric mass-corrections or adjustments To estimate the mass-scaling exponent for the metabolic rate of Argyrosomus species, the data were first temperature-corrected by dividing metabolic rate data by the Arrhenius function.The slope of the linear regression between the natural logarithm of RO2 (temperature corrected) and the natural logarithm of mass was taken as the allometric exponent (α) of the mass scaling relationship for either SMR or MMR data.RO2 data was then mass corrected (MO2) using the mass scaling relationship

Figure S2 :
Figure S2: An example of a full metabolic rate trial at 18 ˚C for Argyrosomus inodorus.Each black point corresponds to a calculated raw metabolic rate (RO2) before chasing (black dashed line).Each red point corresponds to a calculated raw metabolic rate (MO2) post exhaustive protocol and the subsequent recovery.

Figure S4 :
Figure S4: Multilocus genetic tests performed on 74 Argyrosomus species individuals sampled in the study, using STRUCTURE.Green vertical bars indicate Argyrosomus inodorus type individuals while the red bars indicate Argyrosomus coronus types.

Table S2 :
Percentage of Argyrosomus coronus (numbers sampled in parentheses) in the catch composition of the Argyrosomus fishery in the West Coast Recreational Area (WCRA) and Skeleton Coast National Park (SCNP) in Namibia and in the Cunene River mouth (border between Angola and Namibia) (Extracted from Potts et al., 2014b).

Table S3 :
Genetic variability for the resolved Argyrosomus inodorus and

Table S4 :
Summary of multiple lines of evidence for hybridization between Argyrosomus coronus and Argyrosomus inodorus, including morphology, mtDNA COI haplotypes and nuclear microsatellite genotypic assignment using STRUCTURE (for models AD+IAF = admixture with independent allele frequencies; NAD+IAF = no admixture with independent allele frequencies; AD+CAF = admixture with correlated allele frequencies) and NewHybrids.Bold = F2 hybrid.bc = backcross.