Unformatted text preview: mummified elephant seal skull today’s factoid • • Life and Death of an Elephant Seal Colony in Victoria Land Antarc9ca Biologists have used DNA varia9on data from the remains of elephant seals to determine that a thriving colony once exisited in Victoria Land The colony existed between 400 and 7000 years ago May have had up to 220,000 breeding individuals Decline in numbers began 1000 years ago, associated with cooling of Ross sea and expansion of sea ice, which inhibited annual movements of elephant seals to that loca9on hLp://antarc9csun.usap.gov/science/ contentHandler.cfm?id=1852 story posted in Biology in the News on BB • • • • • what is a plant? How did we get from Charales Rhynia Mighty Oak land plants evolved from a clade of green algae that shared (synapomorphies): • Plasmodesmata, – connec9ons between cells joining their cytoplasm • branching growth from the apical 9p of the organism • embryos: egg is retained within parent organism – protec9on from desicca9on other important adapta9ons for terrestrial life • cu9cle (see previous lecture) • gametangia – cases enclosing gametes • pigments to protect against UV damage (see previous lecture) • spore (see various life cycles) walls are thick and contain sporopollenin protein – polymer – helps prevent desicca9on, ro]ng • mutualis9c associa9ons with fungi liverworts and hornworts • remember they are nonvascular, no apical growth, thought to be basal to mosses and vascular plants – basal = diverged anciently (at the base of the tree) rela9ve to other taxa early land plant 9me line • ~500 mya land plants evolve from green algae living in shallow freshwater • lycophytes (club mosses and related groups) and pteridophytes (horsetails, ferns, others) appear 409‐354 mya (Devonian period) • Forests of lycophytes, some 40m tall dominated during the Carboniferous period (360‐300 mya) – dominant land life form for ~200 my – became coal deposits in N. America, Europe, elsewhere land plant fossil record • vascular plants fossilize beLer, appear before nonvascular plants • DNA evidence provides evidence that nonvascular plants predated vascular plants – this is the accepted view • ancient microfossils (see expt. Fig. 28.6) have cellular morphology similar to modern day liverworts Mosses Mosses Mosses Mosses Mosses Mosses Stages of life‐cycle in plants Sporophytes – make SPORES = a diploid(2N) that produces spore(N) Gametophytes – make GAMETES = a haploid(N) makes a gamete(N) “ (N) (N) (N) ” (N) (=> N) (2N) (2N) (2N) How to meet the challenge of the land • Resist drying out/excess radia9on • Support mass against gravity • Get and Transport nutrients/H2O to where needed • Reproduce Mosses have a strategy to meet some of these needs mosses: successful but limited in form • lacked advanced transport mechanism for water, dissolved nutrients – textbook men9ons channel‐forming hydroid cells • may be the ancestral form of tracheids • need water for fer9liza9on – sperm cells need to swim (2 ﬂagella) to fer9lize egg cells • but (see previous slide) haploid spores formed in the sporangium of diploid sporophyte, they are resistant to desicca9on – can survive dry periods before germina9ng to form gametophyte Xylem systems evolved in early vascular plants - Rhynia – only known from fossils (also shown in Fig. 28.9) Xylem consists of tracheids and vessel member cells (two diﬀerent cell types) Eventually Vascular plants evolved secondary cells walls with lignin
From Be]na Selig, Gunilla Borgefors: hLp://www.cb.uu.se/ Lignin is bright green The most abundant organic material on earth aier cellulose (in cell walls of green plants, some algae, also present in some bacteria) what about leaves and roots? • Developmental biologists believe that they evolved in similar ways from similar 9ssues/ structures • but may have evolved at diﬀerent 9mes – shoot system – above ground – root system • develops analogously to shoot system in many ways, specializes for below ground func9ons • rhizomes are stems growing underground to produce new above ground growth nearby – present in Rhynia – roots likely evolved as rhizomes ﬁrst Ferns - (Vascular Plants) – make large (“true”) leaves with extensive vascular supply Tree ferns Cycads are not ferns, they are gymnosperms Fern spore dispersal in air: very eﬀec9ve for an invasive plant • Lygodium microphyllum – "Old World climbing fern" – African/Asian na9ve • currently invading Florida Everglades as a rapidly spreading weed http://www.anbg.gov.au/fern/images/p254.jpg http://upload.wikimedia.org/wikipedia/commons/3/39/ ARS_Lygodium_microphyllum.jpg ...
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- Spring '08
- DNA, Fern, Rhynia, • •