Lectures 3 and 4 Flashcards
Evolutionary Transitions: Jaw Joints and Ear Bones - Early Amniotes
Had 7 bones in lower jaw, including angular and articular
Jaw joint = articular and quadrate
Stapes was already used in sound transmission from external ear, through middle ear, to inner ear
Stapes = columella of other tetrapods
Evolutionary Transitions: Jaw Joints and Ear Bones - Mammals
The jaw was remodeled during the evolution of mammals from non-mammalian synapsids
Only dentary comprises the lower jaw
Jaw joint = dentary and squamosal
2 bones that were formerly part of the jaw joint now incorporated into the middle ear - the articular and quadrate
Mammal Reproduction
Tied to virtually every structural, physiological, and behavioral adaptation of an individual or species
Is of great antiquity (i.e. evolved early)
- Mammary glands
- Milk for nourishing newborn
- Close mother-young bond
- Viviparity evolved later
Male Anatomy
Male Reproductive System:
Testes (male gonads)
-Produce gametes to females
Penis (intromittent organ)
-transport gametes to females
-Internal fertilization
ALL mammals use an INTROMITTENT ORGAN
Spermatogonia undergo spermatogenesis during breeding season
Spermatogenesis is continuous in mammals where there is no breeding season
Saves energy for animals with breeding seasons to only undergo during that time
Reproductive System: Male
Testes may stay internal permanently
Testes may be suspended outside the body cavity in thin-skinned scrotum
- Migrate out of the body cavity at birth permanently
- Migrate out at sexual maturity
- Allows cooling away from the warm body cavity
- Sperm development is hindered by high temperatures
For good spermatogenesis, needs to be COOLER than body temp (98.6); cooer environment descended outside of body, so sperm development is hindered by higher temperatures
Variationin Baculum Morphology
The Baculum is the penis bone (AKA ospenis) found in SOME mammals
Carniverons (dogs, cats, raccoons, seals, sea lions, bats, rats, some primates)
Single bone that supports the penis in intromission
Up to 18” long in Walruses
Female Anatomy
Females Must:
- Manufacture gametes (ova)
- Receive and transport male sperm to the ova
- Nourish developing young during gestation
Females responsible for more than males
Gestation is species-dependent: Anywhere from a couple of weeks to 22 months
Females must ALSO:
- Undergo parturition (birth - or egg laying in monotremes)
- Provide energy-rich milk (lactation)
- Provide protection and support after lactation
Strategy of male mammals: Mate with as many females as possible to spread as many genes as possible
Strategy of females: Be picky about males, need to produce very fit young, mate with males that are most fit
Female Anatomy: Monotremes
Subclass Prototheria
Duplex uterus
-Right and left uteri enter urogenital sinus
Cloaca present
Cloaca: Single opening that empties digestive, urinary, and reproductive tracts
Cloaca is ANCESTRAL trait
Female Anatomy: Metatherians
In addition to paired uteri, they have paired cervices
Pair of uteri enter into vaginal sinu
Duplex cervis (2 cervices)
2 vaginas
-Male metatherians have a forked, biphid penis
Common urogenital sinus
Birth occurs through pseudovaginal canal
In a lot of species, there is NOT a central birth canal; form a pseudovaginal canal just before birth
Female Anatomy: Eutherians
Fallopian tube would enter either left or right uterus
Retain paired ovaries
May retain paired cervix and uterus (duplex) or uteri may be fused (simplex or bicornuate)
-Uteri fused at some point (usually proximally)
Single vagina
Diverged ~300Mya
Amniotes are named for the major derived character of the clade _______, which contains specialized membranes that protect the embryo
Amniotic egg
Amniotic Egg: Allantois
Function: Waste deposit
Disposal sac for certain metabolic wastes produced by the embryo
The membrane of the allantois also functions with the chorion as a respiratory organ
Amniotic Egg: Amnion
Function: Floating environment PROTECTS egg
The amnion protects the embryo in a fluid-filled cavity that cushions agains mechanical shock
Amniotic Egg: Chorion
Function: Gas exchange with environment
The chorion and the membrane of the allantois exchange gases between the embryo and the air. oxygen and carbon dioxide diffuse freely across the shell
Amniotic Egg: Yolk sac
Function: Nutrients
Contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”)
Which of the following groups does NOT have an amniotic egg?
a) “Reptiles”
b) Mammals
c) Amphibians
d) Non-avian dinosaurs
e) Birds
c) Amphibians
In birds, shell is calcified
Leathery in other amniotes
Allantois and chorion are both involved in
Gas exchange
Prototherian (Monotreme) reproduction
Females oviparous
Large oocytes (more yolk) -Eggs are quite large; larger egg = more space for yolk/nutrients
Fertilized in the infundibulum
Mucoid coating added in fallopian tube
Thin shell of ovokeratin added at base of fallopian tube
Second shell membrane added in uterus
-Egg is in uterus of mother for a while before it gets laid/spit out through cloaca
Therian Reproduction
Metatherians (Marsupials)
- Bear nearly embryonic young
- Brief gestation period
- -VERY underdeveloped; born at early stage of development (basically the size of a pinkie finger, only an eye spot)
Eutherians (Placentals)
- Bear anatomically complete young
- -Some placentals able to stand within minutes of being born (anatomically complete)
- Long gestation
- -Development occurs within the womb of the mother
Metatherian Reproduction
Marsupium:
- Abdominal pouch in females
- Only ~50% of marsupial spp. have a pouch
- Echidnas (a Monotreme!) also have pouches
Nipples:
-Number and placement variable
Short gestation, long lactation
Embryonic Development in Metatherians and Eutherians
Fertilization occurs in Fallopian tube
Zygote begins cleavage divisions
-Clump of germ cells is morula
Blastocyst reaches uterus in 3-4 days
Outer layer (trophoblast) adheres and erodes endometrium -Trophoblast causes implantation of embryo
Trophoblast eventually forms placenta
Inner cell mass eventually forms embryo
Fertilization occurs in INFUNDIBULUM in MONOTREMES
Fertilization in METATHERIANS and EUTHERIANS occur just past infundibulum
Double number of cells at each cleavage division
Placenta
Functional connection between fetus and mother
Allows for nutritional, respiratory and excretory exchange
Placenta produces certain hormones
Functions as a barrier for large molecules and bacteria
Varying degrees of contact possible
Placenta Types:
- Chorioallantoic placenta (found in EUTHERIANS)
- Choriovitelline placenta (found in METATHERIANS/Marsupials)
Choriovitelline Placenta
Found in Marsupials
INEFFICIENT
Enlarged yolk sack
Relatively little attachment to developing fetus
Issues:
- Gas exchange problem
- Danger of immune response from mom
- Progesterone doesn’t inhibit FSH “Tyranny of the Estrous Cycle”
Embryo can’t get very big
FSH
Follicle stimulating hormone
Cue for ovum to be released
It prevents another egg from being released
Mom CAN get pregnant again
Can’t support 2 different aged embryos in her uterus, so the gestation period is 2 days less than the estrous cycle
Chorioallantoic Placenta
Found in Eutherians
Villi extend deeply into uterus
Very tight connection between mother and fetus
Eutherians
Hormonal feedback loop prevents formation of new follicle when female is pregnant
Chorioallantoic placenta (VERY efficient)
Trophoblast (prevents immune response by mother to embryo)
Can have Long gestations
Potential for precocial young
Marsupials
“Tyranny of the Estrous Cycle”
-No hormonal feedback loop
Choriovitelline placenta (not very efficient)
NO trophoblast (immune response a potential problem)
Gestation must be short
Extended lactation
young altricial at birth
The marsupial mother: Embryonic Diapause in Macropus rufus
Female red kangaroo has multifaceted reproductive system
2 lateral vaginas meet at urogenital sinus; attached to 2 uteruses. 3rd median vagina used for birth
After 1 week development, embryo goes dormant, lasts until previous young leaves pouch
Mother can concurrently have:
1 developing embryo in uterus
Newborn in pouch
Joey still ebing weaned off milk
Eutherian Reproduction
All eutherians possess a chorioallantoic placenta
- Develops from extra-embryonic membranes
- -Outer chorion, inner vascularized allantois
- Long-lived and highly vascularized
- -Compare with choriovitelline placenta of metatherians
Summary of Female Reproductive System
Monotremes: Cloaca, no placenta (yolk sac and endometrial nourishment), true mammary glands, lack nipples
Marsupials: Cloaca, choriovitilline placenta, true mammary glands, nipples
Eutherians: NO cloaca, chorioallantoic placenta, true mammary glands, nipples
Lactation: Milk Compotision in Eutherians
Remains fairly uniform while lactating
Concentration of milk varies by species
Components of milk CHANGES over course of lactation; starts high in fat and protein; becomes leaner as baby grows
Lactation: Milk Composition in Metatherians
Changes over the course of lactation
Concentration varies little among species at similar stages in lactation ion of milk varies by species
Order Monotremata
Family Tachyglossidae
Echidnas (spiny anteaters)
Found in Australia, Tasmania, and New Guinea
Order Monotremata
Family Ornithorhynchidae
Duck-billed platypus
Found in Eastern Australia and Tasmania
Monotreme Morphology
Beak-like rostrum
Adults are TOOTHLESS
-Have an egg-tooth as babies to break the shell
Sutures disappear
No auditory bulla
Lacrimal and frontal bones absent
Pectoral girdle retaines ancestral features
Monotreme Reproduction
Combine reptilian and mammalian features
Ancestral characteristics
- Yolky egg with shell
- Fetal egg tooth
- Eggs incubated outside mother’s body
- Cloaca
Derived Characteristics
- Multiple chromosomes
- -10X (female), or 5X and 5Y (male)
- Lactation
- -Lack of teats (milk is secreted from skin, young will lap up milk from surface of skin
Cloaca present
Testes abdominal
Mammae lack nipples
Long lactation periods
