Bio 3950 — Autumn 2006

Vertebrate Natural History

Lecture notes, cont’d…..

Mammals —— Life with milk production

Class Mammalia Å 4,400 spp. w/ global distribution. Unique characteristics:

• 4-chambered heart w/ tricuspid valve separating chambers on right side
• anucleate biconcave erythrocytes
• 2 occipital condyles supporting skull; largest rel. brain size/complexity
• complete 2° palate w/ 2 "seals"
• heterodont, diphyodont dentition
• endothermic w/ insulation of hair
• mammary and sebaceous glands

Evolutionary novelties associated with incr. metabolic demand/provision (Diapsida à Synapsida à Therapsida à Mammalia)

• greater cranial muscle mass, esp. around zygomatic arch
• heterodont dentition w/ tooth specialization
• 2° hard palate (eat/breathe simultaneously)
• ventral centering of limbs enhanced locomotory performance
• shorter tail and loss of lumbar vertebrae
• calcaneal heal provides stronger lever for gastrocnemius muscle

3 major groups w/in Class:

Subclass Prototheria — 1 Order, 3 spp.; Australia, New Guinea

• Oviparous (shell gland in oviduct)
• Females incubate eggs; mammary glands lack nipples but young suckle from tufts of ventral hair
• Males lack seminal vesicles and prostate gland; penis everted from ventral wall of cloaca (common urogenital opening).

E.g., duckbilled platypus, echidna

Subclass Theria —non-oviparous mammals

Infraclass Metatheria — 1 Order, Å 200 spp.; most in Southern hemisphere

• Choriovitelline placenta (formed from chorion & yolk sac membrances)
• Viviparous, all spp. w/ altricial young
• Females have marsupium in which young complete development

E.g., koala, kangaroo, tasmanian devil, opossum

Infraclass Eutheria — 20 Orders, global distribution

• Chorioallantoic placenta (formed from chorion & allantois membranes)
• Viviparous, many species w/ precocial young
• Largest cerebrum à reasoning & cognitive processing.

Specializations w/in Class —

1. Hair/fur is dermal outgrowth projecting through epidermis, 2x as strong as bone per unit size (i.e., very elastic); 2 types

• underfur — thick, short, 1° for insulation
• guard hair — long, stiff, 1° for protection

2. Skin glands

• mammary glands — found in all females (& most males) where functional development from ventral thoracic epidermis is homonally regulated (oxytocin, growth hormone); secreted milk high in albumin, lactose, fat.
• sweat glands — epidermal, 1° for thermoregulation, but also ion balance
• sebaceous glands — demal, @ base of hair follicle, secrete waxy oil to moisten hair/fur
• lacrimal gland — secretes isoosmotic fluid to moisten/clean eye
• scent gland (musk) — anal gland for communication, defense, territoriality, & sexual attraction

Loss of all but a few hairs is derived for various functions (e.g., reducing frictional drag in Cetacea, manatees, naked mole-rats).

Alternate functions of hair/fur

• Sensory perception — vibrissae on canids, felids
• Locomotion — rudder width in flying squirrels
• Communication — aposematic (skunks), aggression (canids, felids), sexual dimorphism (primates)
• Specialized function — bristles in suids, quills in porcupine

What can you do with 12 cranial nerves? — mammalian diversity

Body ornamentations

• Giraffe horns — unbranched permanent bone covered w/ skin and fur
• Horns — bony core covered by keratinized epidermis, permanent, unbranched ( e.g., bovids)
• Antlers — bony outgrowth initially covered in vascularized epidermis, branched (e.g., cervids)
• Rhinos — horn entirely of keratin (compacted hair)

Communication mechanisms:

• Visual — predator avoidance (aposematism in skunks) or recognition (stotting, tail flash in Artiodactyla), aggression or submission (hair erection, facial expression or body posturing)
• Chemical — sex attractants (pheromones), individual recognition (usu. sibs or offspring), alarm substances (released under stressed conditions), territorial (E-efficient alternative to physical contact)
• Tactile — grooming reinforces relationship (e.g., primates, canids)
• Auditory — territoriality, aggression, indiv./spp. recognition/location, distress
• Echolocation — spp.- or indiv.-unique use of ultrasonic sounds emitted from larynx (Cetacea) or nose (Chiroptera).

Locomotory adaptations

• Unspecialized — plantigrade, all limbs rel. short & segments of equal length (e.g., ursids, procyonids).
• Cursorial — digitigrade w/ mass centered over middle digit, rel. shorter proximal limb segments w/ more muscle mass (e.g., Artiodactyla)
• Fossorial — plantigrade w/ heavy claws, fusiform body w/ developed musculature (e.g., talpids)
• Aquatic — webbed feet or flippers/fluke, incr. subdermal fat deposits, thick tail base (e.g., Cetacea, pinnipeds, otters)
• Arboreal — long limbs, either opposable thumbs or hooked claws, stereoscopic vision, some w/ prehensile tail (e.g., sloths, primates)
• Aerial — modified hand (homologous w/ Aves) w/ skin membrane spread across digits (ptagium) and tail (uroptagium); bats.
• Volant — dorso-ventrally flattened tail, skin flaps between appendages for gliding (e.g., Glaucomys)
• Saltatorial — rel. lower # of digits and forelimb length, rel. longer tails (used as a counter-balance; kangaroos, wallabies, kangaroo rat.

Digestive Specialization — symbiosis & the 4-chambered stomach

• Most herbivorous mammals are mutualistic w/ bacteria & protozoans that aid in cellulose digestion and have complex stomachs to "re-digest" plant material (ruminants). The rumen temporarily stores & mechanically digests, the reticulum packages for regurgitation as "cud." After chewing the cud, it’s passed to omasum for further mechanical digestion, and then to abomasum for enzymatic digestion.
• Intestinal length correlated w/ diet à ^ herbivory = ^ length.
• Separate urogenital openings except in Prototherians (cloaca retained).

Note, that migration (cues & orientation), adaptations for thermoregulation & mating systems in Mammalia have many similarities w/ those in Aves.

Timing Parturition

• Immediate fertilization and implantation proceed to direct development.
• Delayed fertilization — peak in male spermatogenesis out of synch. w/ follicle maturation; usu. in hibernating Rodentia
• Delayed implantation — copulation results in fertilization, but zygote doesn’t implant in uterine lining (so, development is suspended); can be obligate (e.g., Carnivora) or facultative (EST & PRO regulation of implantation b/c female may be nursing litter from previous mating, e.g., Rodentia, Insectivora).
• Delayed development — suspended development following implantation (e.g., so that late-Summer matings don’t produce offspring in mid-Winter).

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Marvelous morsels mentioning mammals

Morphology & physiological performance

• Size range from 2 g (pygmy shrew) to 140 t (blue whale), > 150x BMR
• Water availability from desert to oceanic; e.g., kangaroo rat extracts most water, produces high [urine] using long loops of Henle in nephron.
• Temp. tolerance from polar (polar bear) to desert, e.g., circulatory shunts and counter-current circulation to minimize core temp. differential w/ environment.
• Speed adaptations include dorso-ventrally flexible spinal column, non-retractible claws, fixed wrist joints; e.g., cheetah @ 90 km hr^-1

Swimming & diving adaptations (all derived characters, esp. in Cetacea)

• nostrils on dorsal aspect of head
• fins/fluke dissociated w/ axial skeleton (pelvis absent)
• ability to collapse lung (prevents nitrogen gas build-up)
• greater tolerance for ^ [CO₂] and ^ [lactic acid] in blood
• greater # of erythrocytes and [myoglobin] in blood
• autonomic decrease in bpm, circulatory shunt to swimming muscles

Social systems in mammals

• Solitary — except during courtship & mating, e.g., ursids
• Herds — concentration around limited resource or increased predator vigilance, usu. w/ temporary hierarchy; e.g., ungulates
• Packs/prides — cooperative foraging for large(r) prey, usu. w/ long-term hierarchy; e.g., felids, canids
• Troops/pods — high levels of social interactions, cooperative foraging, hierarchy sometimes present; e.g., Cetacea, Primates
• Eusociality — reproductively-dominant female w/ surrogate/mid-wife helpers & worker caste to locate and retrieve food; e.g., naked mole rat

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The unity of oppression – the impact of Homo s. sapiens

Characters unique to Homo

• bipedalism – upright posture during locomotion
• increase in rel. brain mass – metabolically expensive, so foraging efficiency had to increase.
• Language – req’d change in breathing control, position/size of larynx

Humans monitoring vertebrate populations

Scan surveys

Mark-recapture surveys – mark in a way that doesn’t affect spp. mobility

Collections

Radio-telemetry – sometimes invasive, but not lethal

Tissue sampling – invasive but not lethal, assoc. w/ DNA analyses

Humans manipulating vertebrate populations

1. Encroachment – habitat manipulation affects area-sensitive species

2. Hunting –

Predator control: Canis, Ursus

Pest control: Odocoileus, Rodentia, Canis, Procyon, Didelphis

Subsistence – kills for food, Bison

Sport – kills for recreation, Odocoileus, Melagris, sciurids, fish, Crotalus

Commercial – kills for profit, mustelids, lagomorphs

3. Commercial harvest – profit-based removal from habitat w/out killing (pet trade, research labs, circuses)

4. Non-native introductions

a) Tilapia zillii (striped tilapia) – imported by gov't/private agencies since '50's for fish ponds and/or controlling aquaphytes, and invert. pests. Effects include displacement of native fish spp. and predation on native aquaphytes. Eradicated from Fla. & Nev., but established populations remain in _ 6 states.

2. Boiga irregularis (brown tree snake) – accidental introduction to Guam via post-WWII troop movements. Presently > 1,000,000 indiv's. (31,000 km^-2). Effects include power outages & extinction/extirpation of > 20 native vert. spp.

What can you do to slow the spp. extinction rate? (acting locally)

1. basics – things you should be doing & encouraging others to do as well:

a) USE LESS STUFF

b) recycle (everything, even if municipality doesn't accept items)

c) reduce your use of fossil fuels for transportation

d) select products for purchase that are environmentally sound

e) compost your yard and vegetable waste

f) weatherize your dwelling to reduce energy demands of temp. control

2. so you wanna call yourself an environmentalist? (the advanced tactics)

a) reduce your use of fossil fuels for power – install/use rechargable batteries, fluorescent/natural lighting, solar water heating, radiant heat

b) carpool when using a car is necessary

c) trade in your gas-guzzler for a more economical & efficient subcompact.

d) capture/redistribute rainwater from gutter downspouts

e) enhance biodiversity and native spp. by eliminating lawns

f) ensure that hazardous household wastes are properly disposed.

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"There is a pleasure in the pathless woods,

There is a rapture on the lonely shore,

There is society, where none intrudes,

By the deep sea, and music in its roar:

I love not man the less, but Nature more."

-- Lord Byron.

PLEASE take responsibility for your actions and how they affect Earth!