Lecture 19 - Adaptations to living in freshwater environments

How animals have adapted to living in freshwater environments: 2). Thermal Adaptations - Biochemical adaptations

-Broad-spectrum enzymes that can function over a wide range of temps. - are little affected by changes in temp. -Several isoforms of enzymes and switch between them as needed. -Express different morphs of the key enzymes at different seasons (e.g. Myosin ATPase (involved in muscle contraction) in fish: expression increases 2-fold when temp. decreases to allow activation of muscles more quickly at low temps.).

Importance of Habitable freshwater

-Can be highly productive areas - support a wide range if species. -Freshwater habitats are highly variable - wide range of environmental conditions. -Freshwater play an important role in the cycling of minerals and nutrients around terrestrial systems. -Play important role on human activity.

How animals have adapted to living in freshwater environments: 3). Respiratory adaptations - If hypoxia cannot be avoided by behavioural mechanism:

-Expand or reduce respiratory surface. -Use higher affinity respiratory pigments. -Regulate ventilation and/or circulation rates: first and quickest response to changing O2 levels. Examples: sponges & rotifers increase movement of cilia; freshwater crayfish increase ventilation of gills; freshwater fish increase opercular pumping.

Challenges faced in Freshwater: 1). Osmotic Concentration

-FW is permanently dilute: 0.01-0.5 ppt or ~ 10mOsm - cells cannot function at these low [conc] of ions. -Unpredictable changes in osmotic [conc]: rainfall, snow/ice melting, evaporation.

How animals have adapted to living in freshwater environments: 3). Respiratory adaptations - Freshwater insects

-Gills are the most common adaptation to insure oxygen uptake.

Ionic and Osmotic Adaptation

-Hypo-osmotic urine: re-absorbs ions from the urine using specialized cells: *Flame cells in 'lower' invertebrates *'Freshwater kidney' in 'higher' invertebrates eg freshwater crayfish.

Ionic and Osmotic regulation in freshwater fish

-Maintain osmotic [conc] much higher (300 mOsm) than freshwater (10 mOsm) -Excrete water in urine -Active uptakes of salts through gills. Similar mechanisms in freshwater invertebrates, but organ of ion uptake is skin.

How animals have adapted to living in freshwater environments: 4). Life History Strategies

-Many species have developed short life cycles with a reduced larval phase: larger eggs, brood pouches. -Larvae are usually large and crawl or swim.

Lotic Waters

-Moving water (e.g. rivers and streams). -Lotic waters fundamentally run downhill: with decrease in flow rate and increase volume and from source to sea.

Challenges faced in Freshwater: 4). Reproduction and Life cycle

-Permanence/transience of habitat. -physiological difficulty of regulating osmotic [conc] in larvae and juveniles (high surface area-to-volume ratio). -Downstream flow (lotic waters).

How animals have adapted to living in freshwater environments: 2). Thermal Adaptations - Behavioural adaptations

-Seek warmer micro-habitats: warmer waters at edge of ponds. -"basking" in the sun in shallow waters.

Lentic Waters

-Still water (e.g. lakes, ponds, wetlands). -Stratification due to variation in O2 levels, light, and temp.

Differences in habitats along length of rivers

-Temperature (altitude, season) -Iron (rainfall and run-offs) -Oxygen levels (water movement and temp.).

Challenges faced in Freshwater: 2). Temperature

-Varies across latitudes/altitudes. -Varies with season. -Unpredictable changes in volume (discharge) = changes the heat capacity of the water, affecting temp. -Will also vary across length of a river.

How animals have adapted to living in freshwater environments: 3). Respiratory adaptations - Adult freshwater insects

2 main air supply systems for use underwater: air bubbles and plastrons. -Plastrons = air bubble constrained in a dense mat of fine water-repellent hairs.

Freshwater

Any body of water with a low salt [conc]. Freshwater salt [conc] 1% of that of seawater. ~10mOsm

How animals have adapted to living in freshwater environments: 1). Ionic and Osmotic concentrations

Living in a very dilute medium with unpredictable inputs from rainfall and terrestrial run-off: -Constantly under threat of gaining water (swelling) and losing ions. -Variable ion composition. -ALL freshwater animals are capable of osmotic regulation.

Challenges faced in Freshwater: 3). Variation in O2 levels

O2 Varies with: -Increasing temp: lakes can loose up to 50% of their O2 over spring/summer. -Water movement: increased movement increases amount of O2 that diffuses into water. -Changes in productivity, i.e. plant photosynthesis: depletes O2.

How animals have adapted to living in freshwater environments: 3). Respiratory adaptations - Behavioural mechanisms

Seeking micro-habitat with higher O2 levels: e.g. many invertebrates move to cooler waters.

How animals have adapted to living in freshwater environments: 4). Life History Strategies - Dormancy of eggs

eg Daphina -eggs develop without fertilization (female only populations favorable conditions) but use fertilization to produce "winter eggs" with a shell that can withstand harsh conditions.