Interspecific differences in early life‐history traits in a species complex of stream‐resident galaxiids

Abstract

Fish differentially provision resources to eggs and larvae to optimise survival during the critical early life-history period. Resource allocation is limited by a trade-off between egg size and fecundity, and the optimal strategy varies with habitat type. This study examines the consequences of egg size differences for the early lifehistories of four closely related galaxiid species which occur in contrasting habitat types on the South Island, New Zealand. Headwater species had substantially larger water-hardened eggs, longer incubation times, and newly hatched larvae were on average up to 41% longer than lower catchment species. Significant interspecific differences in gape diameter, eye diameter and myomere depth were also observed. Swimming ability was positively associated with larval length at hatch. Interspecific differences in length and swimming ability were generally maintained throughout the larval period, despite larvae being reared under relatively benign conditions where many other studies suggest initial differences should disappear. These results demonstrate the consequences of differential maternal provisioning to the egg for larval traits. The larger larvae of headwater species are likely to be more resistant to starvation and have improved foraging ability compared to lower catchment species; traits which are likely to confer them survival advantages in the low productivity, food-scarce environments they occupy. The smaller larvae of lower catchment species are likely to be a consequence of females investing in fecundity in these relatively resource-rich streams.

Life history influences the vulnerability of New Zealand galaxiids to invasive salmonids

“…The high size‐relative fecundity, early onset of maturity and high reproductive effort in ‘fast’ life‐history species such as G. anomalus and G. vulgaris (Jones et al ., ) mean they produce large numbers of larvae (Jones & Closs, in press). Their small larvae, which have poor swimming ability (Jones & Closs, ), become passively dispersed widely across catchments (Jellyman & McIntosh, , ; Jones, ; Jones & Closs, in press). It is likely that these traits facilitate the connectivity supporting the source‐sink metapopulation system in these species (Jones, ; Jones & Closs, in press), enabling them to persist in many salmonid‐invaded reaches (Woodford & McIntosh, ).…”

“…(; Table ). G. anomalus is predominantly found in lower catchment areas and has traits synonymous with a fast life history – small egg and larval size, high fecundity, early maturation, small adult body size and high reproductive effort (Jones & Closs, ; Jones et al ., ). Populations of this species also produce large numbers of widely dispersive larvae, traits which drive source‐sink metapopulation dynamics in this (Jones, ; Jones & Closs, in press), and another closely related species with similar life‐history characteristics ( G. vulgaris sensu stricto ; Woodford & McIntosh, ).…”

“…Populations of this species also produce large numbers of widely dispersive larvae, traits which drive source‐sink metapopulation dynamics in this (Jones, ; Jones & Closs, in press), and another closely related species with similar life‐history characteristics ( G. vulgaris sensu stricto ; Woodford & McIntosh, ). In contrast, the headwater species, G. pullus and G. eldoni , exhibit traits consistent with a slow life history – large eggs, large larvae, low size‐relative fecundity, large body size and delayed maturation (Jones & Closs, ; Jones et al ., ). These traits are associated with low numbers of offspring and minimal dispersal of larvae, and as these traits limit population connectivity, these species are likely to form isolated population structures (Jones, ; Jones & Closs, in press).…”

“…These traits are associated with low numbers of offspring and minimal dispersal of larvae, and as these traits limit population connectivity, these species are likely to form isolated population structures (Jones, ; Jones & Closs, in press). G. depressiceps , which occurs in streams with intermediate habitat characteristics, has intermediate life‐history traits, and likely also population structure, relative to those of the other species (Jones, ; Jones & Closs, , in press; Jones et al ., ).…”

“…For input into the GLM, life history was coded as a categorical variable; G. anomalus was coded as 1 – ‘fast’ life history, G. depressiceps as 2 – ‘intermediate’ life history, and G. pullus and G. eldoni were coded as 3 – ‘slow’ life history, following interspecific differences previously found (Jones, ; Jones et al ., ; Jones & Closs, ; Table ). Environmental information for reaches was extracted from FENZ, which contains physical habitat information for stream networks in New Zealand (Leathwick et al ., ).…”