Primal Origin of the Freshwater Invertebrates

1. Primal Origin of the Freshwater Invertebrates Jerry L. Kaster What is theGeologic Time-Scale History of Freshwater Invertebrates? What are theColonization Routes of the Freshwater Invertebrates? Habitat Corridors Continental Corridors Regression-Transgression Route associated competitive strategies What was the Role ofK+ Scavenging in Establishing a Brooding Fauna? Bryant 1775

2. What is theGeologic Time-Scale History of Freshwater Invertebrates? Assumptions First, the contemporary marine and freshwater faunas are more ecesis compatible than are faunas not contemporary. Second, marine taxa with a high survival rate (implying gene pool breadth) on a geological time scale are more likely to colonize new habitats, both marine and freshwater, than taxa with a low survival rate. By example, the extinct trilobites would have a zero probability for a modern colonization of freshwaters; whereas extant marine forms without a contemporary freshwater counterpart, such as branchiopods or echinoderms would score a probability for a modern occurrence in freshwaters. The fact that the latter two forms do not now exist in freshwater does not rule out the possibility that they may colonize in the future. Third, the predicted probability of occurrence for a ancestral freshwater fauna is a recapitulation of its descendant freshwater fauna.

3. PFPt= ((MPt + FPt)  2)  MSP PFPt  1=((MPt 1+ PFPt) 2)  MSP PFPt  2= ((MPt 2+ PFPt 1) 2)  MSP PFPt  3= … Where: PFPt = Predicted freshwater probability MPt = Extant marine taxon probability FPt = Extant freshwater taxon probability MPt-n = Fossil marine taxon probability (mainly Raup 1976)   t = Faunal geological period, where 1 = Cenozoic; 2 = Mesozoic; 3 = Palaeozoic; 4 = Precambrian MSP = Marine taxon survival probability (Easton 1960): Crustacea (0.930), Gastropoda (0.821), Annelida (0.973), Pelecypoda (0.423), Porifera (0.560), Ectoprocta (0.504), Echindermata (0.270), and Brachiopoda (0.015).

11. Devonian 21% Ordovician 22% Mesozoic Fauna 230 - 63 Permian 95% Cretaceous 75% Triassic 20% Paleozoic Fauna 600 - 230 TIME

12. Are there too many species clustered in too few Phyla?

13. Idealized Probabilistic Signature of the Freshwater Invertebrate Fauna Pm=0.81 P R O B A B I L I T Y Pm=0.72 Pm=0.61 Pm=0.53 Pm=0.51 Extant Fauna Precambrian Fauna Mesozoic Fauna Cenozoic Fauna Paleozoic Fauna

16. Suppositions A shift along the time series is characterized by an overall rise in dominance of fewer taxa with high probable occurrence. Communities of greater horizontal energy-material exchange have more rare species and should be distinguished by greater evolutionary innovation. Catastrophic Permian community disruption reduced rare taxa, with common taxa gained dominance (reduced diversity). The K-T disruption increased rare taxa relative to common taxa (increased diversity).

17. What were theColonization Routes of the Freshwater Invertebrates? Immigration Routes Habitat Corridors SeaLandFreshwater (pulmonate snails, insects, mites) Sea EstuaryFreshwater (zebra mussels) Sea PsammolittoralPhreaticFreshwater (protozoa; micrometazoans) Sea MarshFreshwater (amphipods)

18. Immigration Routes Route associated competitive strategies Continental Corridors Equatorial ContinentalVon Martens, 1857 Shotgun approach: Typical r-strategists. Large pool of tropical species with pelagic larvae. Polar Continentalde Guerne & Richard, 1892 Finesse approach: Typical K-strategists. Small pool of polar species with brood representing a pre-adapted life cycle to freshwater.

19. S H E D D I N G F A U N A B R O O D I N G F A U N A 15% 85% Polar Lake Continent Lake 85% Equatorial 15%

20. S H E D D I N G F A U N A B R O O D I N G F A U N A 15% K 85% Polar Increased Habitat Lake Continent Lake Decreased Habitat Equatorial 85% 15% r “Regression Period”

21. B R O O D I N G F A U N A S H E D D I N G F A U N A 15% 85% K Polar Decreased Habitat Lake Continent Lake Increased Habitat Equatorial 85% 15% r “Transgression Period”

22. Why do freshwater forms lack pelagic larvae? Broad statements (e.g., Neeham 1930; Pennak 1953, 1963, 1985) of ion/osmoregulation provided the framework for its general acceptance of the marine to freshwater transition. Abundant suggestions: Ionic - Osmotic gradiant imbalance Energy expenditure to stay afloat Poor pelagic nutrient resources Others Brooding K-strategist Fauna Keen competitors “fill the barrel”; Shedding r-strategist fauna poorly colonize a “full barrel”

23. What was the role ofK+ scavenging in establishing a brooding fauna? Ionic K+ Bottleneck Most cations and anions are regenerated in the epilimnion, while K+ shunts to the benthos. Ca2+ Mg2+ Na+ HCO3 CO32- SO42- Cl- K+ Earth leaches K+ : Na+ = 1 K+ is readily absorbed to soil particulates and thus there is less K+than Na+ in sea water (K+ : Na+ = 0.021) and freshwater (K+ : Na+ = 0.028) K+ is preferentially incorporated into the crystaline lattice of minerals

24. Marine invertebrate K+ levels are similar to sea water medium: Sea water K+ = 9.96 mM/l vs. inverts = 11.56 mM/l (ratio = 0.86) Freshwater invertebrate K+ levels are much higher than the freshwater medium: Freshwater = 0.03 mM/l vs. inverts = 4.75 mM/l (ratio = 0.0063) Benthic sediment K+ =13.8 mM/l vs. 4.75mM/l (ratio = 2.9) Bottleneck is at the late embryo (yolk K+ cache depleted) or at the early larval stage (must shift to high [K+] particle feeding). K+ is necessary for membrane function, especially in excitatory tissue such as muscle and nervous tissue.

25. Suppositions Immigration of K-strategist, marine brooding invertebrates to freshwater largely followed a polar corridor. The de novo evolution of muscle and nervous systems of the primal metazoans (protozoan-metazoan megaleap) required high benthic K+. A “K+ bottleneck” during early life history stages is suggested as a critical factor that regulates freshwater colonization success. Metazoan de novo “K+ scavenging” may have lead to herbivory and “K+ predation” to predation.