Brady K. Quinn

Seascape genomics provides evidence for thermal adaptation and current-mediated population structure in American lobster (Homarus americanus).

Investigating how environmental features shape the genetic structure of populations is crucial for understanding how they are potentially adapted to their habitats, as well as for sound management. In this study, we assessed the relative importance of spatial distribution, ocean currents and sea surface temperature (SST) on patterns of putatively neutral and adaptive genetic variation among American lobster from 19 locations using population differentiation (PD) approaches combined with environmental association (EA) analyses. First, PD approaches (using bayescan, arlequin and outflank) found 28 outlier SNPs putatively under divergent selection and 9770 neutral SNPs in common. Redundancy analysis revealed that spatial distribution, ocean current‐mediated larval connectivity and SST explained 31.7% of the neutral genetic differentiation, with ocean currents driving the majority of this relationship (21.0%). After removing the influence of spatial distribution, no SST were significant for putatively neutral genetic variation whereas minimum annual SST still had a significant impact and explained 8.1% of the putatively adaptive genetic variation. Second, EA analyses (using Pearson correlation tests, bayescenv and lfmm) jointly identified seven SNPs as candidates for thermal adaptation. Covariation at these SNPs was assessed with a spatial multivariate analysis that highlighted a significant temperature association, after accounting for the influence of spatial distribution. Among the 505 candidate SNPs detected by at least one of the three approaches, we discovered three polymorphisms located in genes previously shown to play a role in thermal adaptation. Our results have implications for the management of the American lobster and provide a foundation on which to predict how this species will cope with climate change.

Effect of temperature on development rate of larvae from cold-water American lobster (Homarus americanus)

The duration of the larval phase of the American lobster influences the distance larvae drift, and thus the potential settlement and recruitment patterns of lobsters to local populations and fisheries. The duration of larval stages is influenced by temperature, with warmer temperatures resulting in faster development and shorter stage duration. The quantitative relationship between temperature and duration of larval stages has been previously investigated, but only for lobsters originating from relatively warm-water regions. We examined the effects of temperature on stage duration for lobster larvae originating from a cold-water region, the northern shore of the Gaspe Peninsula in the northern Gulf of St. Lawrence, Canada. We reared larvae individually using a new experimental apparatus with automated movement of culture containers to facilitate water exchange. We compared observed duration of larval stages for these cold-water source larvae to durations in previous studies that used warmer-water source larvae. We observed 38% shorter development times at the coldest temperature used (10°C) and 47, 50, and 100% longer development times at warmer temperatures (14, 18 and 22°C, respectively) than at the same temperatures in previous studies of warm-water larvae, suggesting potential geographic variation in the functional relationship between temperature and larval development time. Given these results, future research should examine this question in more detail, to enhance understanding of lobster ecology and population dynamics across the species’ range.

A critical review of the use and performance of different function types for modeling temperature-dependent development of arthropod larvae.

Temperature-dependent development influences production rates of arthropods, including crustaceans important to fisheries and agricultural pests. Numerous candidate equation types (development functions) exist to describe the effect of temperature on development time, yet most studies use only a single type of equation and there is no consensus as to which, if any model predicts development rates better than the others, nor what the consequences of selecting a potentially incorrect model equation are on predicted development times. In this study, a literature search was performed of studies fitting development functions to development data of arthropod larvae (99 species). The published data of most (79) of these species were then fit with 33 commonly-used development functions. Overall performance of each function type and consequences of using a function other than the best one to model data were assessed. Performance was also related to taxonomy and the range of temperatures examined. The majority (91.1%) of studies were found to not use the best function out of those tested. Using the incorrect model lead to significantly less accurate (e.g., mean difference±SE 85.9±27.4%, range: -1.7 to 1725.5%) predictions of development times than the best function. Overall, more complex functions performed poorly relative to simpler ones. However, performance of some complex functions improved when wide temperature ranges were tested, which tended to be confined to studies of insects or arachnids compared with those of crustaceans. Results indicate the biological significance of choosing the best-fitting model to describe temperature-dependent development time data.

A test of the general occurrence and predictive utility of isochronal, equiproportional, 'variable proportional', and 'mixed' development among arthropods

ABSTRACT In isochronal (ICD) and equiproportional development (EPD), the proportion of total immature (egg, larval, and/or juvenile) development spent in each stage (developmental proportion) does not vary among stages or temperatures, respectively. ICD and EPD have mainly been reported in copepods, and whether they occur in other arthropods is not known. If they did, then rearing studies could be simplified because the durations of later developmental stages could be predicted based on those of earlier ones. The goal of this study was to test whether different taxa have ICD, EPD, or an alternative development type in which stage-specific proportions depend on temperature, termed ‘variable proportional’ development (VPD), and also how well each development type allowed later-stage durations to be predicted from earlier ones. Data for 71 arthropods (arachnids, copepod and decapod crustaceans, and insects) were tested, and most (85.9 %) species were concluded to have VPD, meaning that ICD and EPD do not occur generally. However, EPD predicted later-stage durations comparably well to VPD (within 19-23 %), and thus may still be useful. Interestingly, some species showed a ‘mixed’ form of development, where some stages’ developmental proportions varied with temperature while those of others did not, which should be further investigated. Highlights Whether arthropod development is generally isochronal or equiproportional was tested Developmental proportions of most species’ stages varied with temperature Many species had ‘mixed’ development between variable and equiproportional types The general occurrence of isochronal and equiproportional development was rejected Equiproportional development did make reasonable predictions of stage durationsHighlights Whether arthropod development is generally isochronal or equiproportional was tested Developmental proportions of most species’ stages varied with temperature Many species had ‘mixed’ development between variable and equiproportional types The general occurrence of isochronal and equiproportional development was rejected Equiproportional development did make reasonable predictions of stage durations ABSTRACT In isochronal (ICD) and equiproportional development (EPD), the proportion of total immature development spent in each stage does not vary among temperatures or stages, respectively. ICD and EPD have mainly been reported in copepod crustaceans, and whether they occur in other arthropods is not known. If they did, then rearing studies could be simplified because the durations of later developmental stages could be predicted based on those of earlier ones. In this study, published data for 71 arthropods (arachnids, copepod and decapod crustaceans, and insects) were tested to objectively determine whether they had ICD, EPD, or an alternative form of development in which stage-specific proportions depend on temperature, termed ‘variable proportional’ development (VPD). How well ICD, EPD, and VPD could predict later-stage durations from earlier ones was also assessed. Most (85.9 %) species were concluded to have VPD, meaning that ICD and EPD do not occur generally among arthropods. However, EPD predicted later-stage durations comparably well to VPD (within 19-23 %), and thus may still be useful in arthropod development studies. Interestingly, some species showed a ‘mixed’ form of development, where some stages’ developmental proportions varied with temperature while those of others did not; these findings should be further investigated.

Dramatic decline and limited recovery of a green crab (Carcinus maenas) population in the Minas Basin, Canada after the summer of 2013

This paper reports the results of a ten-year monitoring program of an Atlantic Canadian population of green crabs, Carcinus maenas, in the Minas Basin of the Bay of Fundy. Intertidal densities, sex and reproductive ratios, juvenile recruitment, subtidal catch-per-unit-effort (CPUE), and sizes of crabs in this population were recorded from 2008 to 2017. In 2013 intertidal densities, mean crab sizes, subtidal CPUE, and proportions of crabs mature and reproducing all dramatically decreased to all-time lows, and large crabs virtually disappeared from the population. From 2014 to 2017 the population partially recovered but remained in an altered state. Potential causes of interannual changes to this population were investigated by correlating intertidal densities to 257 monthly environmental variables and performing stepwise multiple regression analyses. Crab densities in a given year were best explained by potential settlement during the summer and the maximum sea-surface temperature during March of the same year. However, potential roles of other factors (e.g., autumn winds, summer temperatures, North Atlantic Oscillation index) could not be ruled out. Changes in abundances of other species in the area, particularly predators and prey of green crabs, have also been observed and present possible alternative causative agents that should be investigated. Populations of other marine species in the Gulf of Maine-Bay of Fundy region within which the Minas Basin is situated have also been reported to have undergone dramatic changes in and after 2013, suggesting the occurrence of some oceanographic event or regime shift in the region. Declines to the monitored crab population in this study may have resulted from this same 2013 event. These observations have implications for recruitment to marine populations in this region.