Egg  Juvenile instars  (Pupa)  Aquatic Insect Life Cycles – variable responses to multiple selective forces Females can lay eggs all at once (short-lived)or multiple times (longer-lived) Eggs can hatch: Immediately  single juvenile cohort Delayed, then all at once Continuously  multiple cohorts Adults can emerge: synchronously asynchronously (all at once) (spread over time) Aquatic Terrestrial Autumn Winter Spring Summer Egg  Juvenile instars  (Pupa)  GROWTH & DEVELOPMENT Adult EMERGENCE Time Temperature

EVOLUTION – maximizes individual fitness Aquatic Terrestrial Autumn Winter Spring Summer Egg  Juvenile instars  (Pupa)  GROWTH & DEVELOPMENT Adult EMERGENCE Eggs can hatch: Immediately  single juvenile cohort Delayed, then all at once Continuously  multiple cohorts Adults can emerge: synchronously asynchronously (all at once) (spread over time) Females can lay eggs all at once (short-lived)or multiple times (longer-lived) EVOLUTION – maximizes individual fitness  maximize growth (g) and minimize mortality risk (µ) Why maximize g? How to maximize g? Avoid competition? Larger female size  more eggs

What are sources of mortality risk? Aquatic Terrestrial Autumn Winter Spring Summer Egg  Juvenile instars  (Pupa)  GROWTH & DEVELOPMENT Adult EMERGENCE Eggs can hatch: Immediately  single juvenile cohort Delayed, then all at once Continuously  multiple cohorts Adults can emerge: synchronously asynchronously (all at once) (spread over time) Females can lay eggs all at once (short-lived)or multiple times (longer-lived) How minimize µ? What are sources of mortality risk? Biotic Abiotic Juvenile (aquatic) Predation (invertebrates, fish, predator numbers) Disturbance (frequency and intensity) Adult (terrestrial) Predation (insects, spiders, birds) Air temperature (limited aerial season) These factors can vary a lot in different streams and regions!

Upshot: Over evolutionary time species have “balanced” the interacting selective factors that influence growth and mortality of both juveniles and adults in an attempt to maximize fitness. This results in a very wide wide range of life cycle strategies, including: - number of generations per year - egg development time and synchrony of hatching - timing and synchrony of adult emergence These strategies can sometimes vary within a species from stream to stream (or region), reflecting the local environmental selection forces that affect the balance of growth and mortality in the juvenile and adult life stages.

Temperature Temperature is important because it: (1) directly controls metabolic rates of ectothermic organisms (invertebrates, fish) Affects growth and development Sets species ranges (latitude and altitude) Species adapted to different temperatures (2) controls dissolved oxygen concentrations (3) is relatively predictable over annual cycle and can provide an evolutionary cue for adaptation Temperature and thermal regimes

Thermal optima are species-specific Differences in species growth rates (Fig. 5.18) Geographic range reflects thermal optima and tolerances (Fig. 7.5)

Also true for fish

Most aquatic species have positive growth over the winter - unlike terrestrial insects (resting eggs or adult diapause) Some species extremely cold-adapted (Fig. 6.12 (Ward 1992)) - even under ice!

Insect Eggs When laid, they can Phenotypic Plasticity a) all hatch immediately b) hatch over time (Fig. 3.17) c) delay hatching (diapause = state of arrested metabolism) Some eggs require cold winter temperature to break diapause Phenotypic Plasticity e.g., some stoneflies perennial streams – eggs hatch immediately intermittent streams – diapause for 9-11 months How much flexibility? Genetic vs. Phenotypic? For most species, don’t know

What happens when temperature changes? Change in thermal regime  change in cues Example: Hypolimnetic (deep) release Dam on Saskatchewan River, Canada Many aquatic insects in far North have winter egg diapause. Rising spring temps after ice-out are required to break diapause [Fig. 3.14] 4°C Dam warms winter water temp. to 4°C for 10s of kilometers Biotic response: 30 genera and 12 families eliminated  1 family remains! (any guesses?)

Growth rate and development: The elaboration of new cells and tissue by an organism Development: The gradual increase in complexity of an organism’s cellular and tissue organization For aquatic insects, culminates in production of adult tissues (wings and gonads) Note: There can also be strong selection for reducing development time to produce more than one generation per year (i.e., even if adults are smaller), especially in environments where likelihood of juvenile mortality is high. More later; now focus on growth. (previous examples of variable voltinism)

Adult body size depends on growth rate, which is temperature dependent If you extend the temperature axis out (warmer), you’ll see a peak (and then decline) in growth rate for each species Figure 10: Same insect species in 2 different streams in the same catchment. For this species, which stream has a more “optimal” temperature?

Growth rate and development: High temp  high metabolism so high respiration loss (metabolic heat) Low Temp  slow metabolism and low growth potential, available energy allocated to adult tissue There is an optimal temperature that maximizes adult body size Established experimentally for several insect species by Vannote and Sweeney (1980) Consider an insect species that must complete development in a fixed time (e.g., univoltine) Small body size because most energy to adult tissue Small body size because high maintenance costs (cellular respiration cost) Temperature Adult body size (growth) Energy to maintenance (resp. loss) Energy to adult tissue

Thermal Equilibrium Hypothesis (Vannote & Sweeney 1978) The optimal thermal regime for species maximizes adult body size (and fecundity) metabolic efficiency population abundance Where in a species’ geographic range would individual body size and population size be greatest?

Center of the species range! Why? Temperature Adult body size (growth) Energy to maintenance (resp. loss) Energy to adult tissue Small body size because most energy to adult tissue Small body size because high maintenance costs (cellular respiration cost) What environmental factors might be complicate this expectation?

Adult emergence: If temperature too cold, then what? Juveniles develop adequately to become sexually mature If temperature too cold, then what? 1) delay maturation, e.g., go from bivoltine to univoltine -- not all species can do this 2) population cannot persist locally Species differ in timing a) fixed temperature of emergence [Fig. 7.13 Sweeney et al. 1992] What is Advantage? (Hint: cue) b) fixed number of degree-days > 0°C [draw on board]

Photoperiod can also be a trigger Why? good predictor of air temperature for adult May be interaction between water temp and photoperiod ? 2 Types of emergence: Synchronous, i.e., all adults appear within a few hours Mayflies - Adults don’t feed Evolutionary reason for synchronous emergence? swamp predators find mate WHY LATER EMERGERS SMALLER? NOT OPTIMAL TEMPERATURE, MORE RESPIRATORY LOSSES Asynchronous, i.e., adults emerge over time Often variation in size of adult Later emergers usually smaller (Fig. 10) possibly because growth rates in stream are not same for all individuals (depends on food acquired) and smaller individuals may wait longer to emerge so they can close the gap in body size yet still find an aerial mate.

What determines thermal regime for a stream? Stream thermal regime depends on environmental and landscape “setting” (Fig. 3.1 (Giller & Malmqvist 1998)) Environmental controls on stream water temperature

Also, thermal regime has components or features that influence growth and development (Fig. 6.1 (Ward 1992)) [note similarity to flow regime components] Environmental Controls Biologically-important components of the thermal regime

Stream temperatures vary with latitude: and position in a stream network

For several streams in the same catchment: Why different thermographs? Which has more degree-days >0 per year? Hint Note: Multiply Y-axis by 10

3 Types of life cycles (1) Slow Seasonal (2) Fast Seasonal Seasonal cycles immatures within species of roughly similar age (“cohorts”) (1) Slow Seasonal (2) Fast Seasonal Nonseasonal individuals of several ages are present at all times. (3) Non-seasonal

3 Types of life cycles [Fig. 5.2, Merritt & Cummins 1996] (1) Slow Seasonal Eggs hatch quickly, juveniles grow slowly, maturity in ~1, 2, 3 years Species may have extended hatching period Examples -- many univoltine stoneflies, some mayflies and caddisflies Where adaptive? Stable, perennial streams time instars

3 Types of life cycles (2) Fast Seasonal Long egg or juvenile diapause, followed by rapid growth to maturity Some species emerge in Spring, Summer, Fall Where adaptive? Stable, perennial streams to avoid competition with similar species Streams with short growing period Intermittent streams Perennial streams with competitors present (e.g., Anagapetus bernea) time instars

3 Types of life cycles (3) Non-seasonal - Where adaptive? Many size classes present overlapping cohorts of multivoltine species (chironomids) poorly synchronized (extended mating/egg-laying) species life cycle spans > 1 yr (stoneflies, dobson flies) - Where adaptive?  In frequently disturbed streams with high juvenile mortality (“bet hedging” life history strategy) In cold, stable streams that require more than one year to complete life cycle. time instars

In cold weather (e.g., February) you can find small aerial aquatic insects along Poudre R. (midges, Chironomidae) How do they survive? Which life cycle type would you put them in? What kind of voltinism would they exhibit? What emergence cue would they use?

Functional Feeding Groups (Cummins 1973) Invertebrates that obtain food resource in similar way Main Functional Groups Shredder Eat coarse particulate organic matter (CPOM, > 1 mm) Collector-filterer Eat suspended fine particulate organic matter (FPOM, < 1mm) Collector-gatherer Eat sedimentary (benthic) FPOM Grazer Eat algae, microbial biofilm Predator