BIOLOGY 457/657 PHYSIOLOGY OF MARINE & ESTUARINE ANIMALS May 3, 2004 BIOLOGICAL RHYTHMS IN THE SEA

Introduction Features of Endogenous, Biological Rhythms Are pervasive, ubiquitous features of animals (& plants) Require endogenous mechanisms that have properties like clocks Vary in strength and persistence: Exogenous rhythm - requires continuous external cycles “Hourglass” rhythm - continues for a single cycle in the absence of the external cycle Endogenous rhythm - persists indefinitely in constant conditions Evidence for their truly endogenous origin is now certain, including some of the genes that contribute to the periodicity and timing. Experiments have demonstrated that some endogenous rhythms continue in orbiting satellites or at the South Pole!

Periodicities of Biological Rhythms The diversity of natural cycles in the sea lead to the presence of a number of periodicities in natural rhythms of marine animals. Tidal rhythm: period is ~12.4 h Circadian rhythm: period is ~24 h Lunadian rhythm: period is ~24.8 h Semilunar rhythm: period is ~14.8 d Lunar rhythm: period is ~29.5 d Annual rhythm: period is ~365 d

Properties of Endogenous Rhythms Require a synchronizer or “zeitgeber”. In free-running conditions, the period is approximate. Hence the prefix “circa”. A rhythm with a period near 24 h is “circadian”, while one with a period near 12.8 h is “circatidal”. Organisms may have several rhythms running in parallel, all with different phases. Are temperature-compensated. May change period in the presence of some drugs or chemicals (e.g. D 2 O).

Examples of Rhythmicity in Gonyaulax In Presence of External LD Cycle

Examples of Rhythmicity in Gonyaulax The Glow Rhythm in Constant Conditions Images/gony.gif

Examples of Rhythmicity in Gonyaulax All Rhythms in Constant Conditions

Temperature Compensation of Endogenous Rhytnms

Effects of Deuterium Oxide (D 2 O)

Activity Rhythms in Crabs The “actograph”

Activity Rhythms in Crabs Data collected from Sesarma reticulatum

TERMINOLOGY AND ABBREVIATIONS Types of cycles: LD - alternate light and dark, as in “LD 12:12” LL - constant light DD - constant dark CC - constant conditions (generally, DD with constant temperature) Free-run: The expression of an endogenous rhythm in CC Periods: T – the period of the zeitgeber τ – the period of the endogenous cycle Phases: φ – the phase of the biological rhythm Δφ – change in phase of the biological rhythm ψ – phase difference between zeitgeber and the biological rhythm Pacemaker: The biological structure that provides timing; the internal “clock” or oscillator

TYPES OF RHYTHMS IN MARINE ANIMALS Short-Period Rhythms: Circadian & Circatidal Numerous examples in marine animals – activity, color change, metabolic rate, vertical migration, egg release, visual sensitivity, orientation (see earlier examples in Gonyaulax) Tidal Rhythms – result from the influences of the sun and moon Lunar month: 29.5 d Spring-Neap Cycle: 29.5/2 = 14.8 d (twice a month) Lunar day: 24 h + 24/29.5 h = h Tidal cycle (semidiurnal): 24.8/2 = 12.4 h

Mixed Circadian and Circatidal Rhythms (Earlier example from Sesarma reticulatum)

CIRCATIDAL RHYTHMS: Example From an Intertidal Organism Results 252b1d30.jpg

CIRCATIDAL RHYTHMS: Alternate Amplitude Reflects Natural Tides

CIRCATIDAL & CIRCADIAN RHYTHMS: Frequently are Involved With Reproduction

hemigrapsus.jpg

SYNCHRONIZATION OF TIDAL RHYTHMS (1) Rhythmic Shaking

SYNCHRONIZATION OF TIDAL RHYTHMS (2) Rhythmic Salinity Cycles

SYNCHRONIZATION OF TIDAL RHYTHMS (3) Rhythmic Pressure Cycles floor2/img/krab_b.jpg

SYNCHRONIZATION OF TIDAL RHYTHMS (4) Temperature Shock

VERTICAL MIGRATION RHYTHMS Circadian Examples

VERTICAL MIGRATION RHYTHMS Circatidal Examples

RHYTHMS IN VISUAL FUNCTION Example 1: Limulus polyphemus The rhythm in the figure is from the electroretinogram (ERG) in the compound eye. The rhythmicity may persist for years in constant dark. The greatest response (& sensitivity) is at night. soma.npa.uiuc.edu/courses/ physl341/limulus.1.jpg

RHYTHMS IN VISUAL FUNCTION Example 1: Limulus polyphemus The rhythm is synchronous is all 5 types of photoreceptor found in Limulus (2 compound eyes, median eye, ventral eye, and caudal photoreceptor).

RHYTHMS IN VISUAL FUNCTION Example 1: Limulus polyphemus Synchronization requires efferent output from the brain.

RHYTHMS IN VISUAL FUNCTION Example 2: Aplysia Note synchronization in the numbers of action potentials produced in constant darkness (the rhythm peaks during the day, unlike that of Limulus, which reveals the greatest sensitivity at night). learningII02 /Slide4.JPG

LONG-PERIOD RHYTHMS Lunadian and Spring:Neap Cycles

LONG-PERIOD RHYTHMS Lunadian and Semilunar Cycles photos/midge.JPG

LONG-PERIOD RHYTHMS An Example of an Annual Cycle Resting cysts of our old friend, Gonyaulax, were collected in the field and stored at 4 degrees C. Samples were tested for percent germination at intervals throughout the next 3 years.