BIL160 Final Exam Giovanni Hanna- Spring 2026

Lophotrochozoans are protostomes or deuterostomes

Protostomes (they develop the mouth first in embryonic development)

Two larval features of lophotrochozoans

Trochophore larva (a tiny swimming larva covered in cilia); Lophophore (a ring of ciliated tentacles used for feeding)

What does the lophophore do

Uses cilia to create water flow and trap food particles

General traits of flatworms (platyhelminths)

Flat body (helps with diffusion); blind gut (only one opening); no circulatory or respiratory system; bilateral symmetry; simple nervous system

Why parasitism is considered an adaptation

Parasites evolved special body structures and life cycles through natural selection to live off hosts (not a choice, it's built into them)

Has parasitism evolved once or many times

Many times independently in different groups

Why many parasites use multiple hosts

Helps them spread, access more resources, avoid immune systems, and reach their final host

Cestode (tapeworm) adaptations

Scolex (head) with hooks/suckers to attach; no digestive system (absorb food through body); body segments full of reproductive organs

Where most mollusks live

Mostly in marine (ocean) environments

Why oceans have more mollusks

Oceans are stable, have lots of habitats, and have existed longer → more time to evolve diversity

3 main parts of a mollusk body

Muscular foot (movement); visceral mass (organs); mantle (covers body and can make shell)

Common mollusk evolutionary change

Loss or reduction of shell (like in slugs and octopus)

Phenotype vs genotype loss

Losing a trait doesn't mean the gene is gone—it might just be turned off

Cone snail hunting adaptation

They shoot a harpoon-like tooth that injects venom

How cone snail venom works

Contains strong neurotoxins that quickly paralyze prey

Cone snail toxin characteristics

Made of small proteins; each species has a mix ("cocktail"); targets specific nerve channels

Why cone snail venom is so diverse

Genes duplicated and mutated over time → lots of different toxins

Why cone snail venom is useful to humans

Very specific → good for making drugs (ex: pain medication like Prialt)

Did mollusks evolve one eye type or many

Many different eye types evolved (cup eyes, camera eyes, etc.)

Why similar eyes evolve multiple times

Same genes can be reused and slightly changed → leads to similar solutions (convergent evolution)

Echinoderm symmetry

Start as bilateral larvae but become radial as adults

Why echinoderm symmetry is important

Shows evolution changed body plan from bilateral ancestor

Echinoderm key features

Water vascular system (movement); tube feet; hard internal skeleton made of calcium plates

Pedicellariae

Small pincer-like structures that clean, protect, and catch tiny prey

Cephalochordates

Basic chordates (like lancelets) that share traits with us but lack a true brain and complex organs

Chordate defining traits

Notochord; dorsal hollow nerve cord; pharyngeal slits; post-anal tail

Why tunicates are interesting

Their larvae look like chordates but adults lose most of those traits

Escape variants

Viruses mutate so they can avoid the immune system and infect again

What fast-evolving pathogen trees look like

Long trunk with short branches (most lineages die quickly)

Red Queen hypothesis

Hosts and pathogens are constantly evolving against each other like an "arms race"

Why sex is important (Red Queen)

It creates genetic variation so organisms can keep up with evolving pathogens

MZT (maternal to zygotic transition)

The embryo switches from using mom's mRNA to its own DNA

Why MZT matters

Important for proper development

Lott lab discovery

There are core genes used in development that are conserved across species

Maternal vs zygotic genes

Maternal = more similar across species; zygotic = more different

DMIs (Dobzhansky-Muller incompatibilities)

When genes that evolved separately don't work together in hybrids

Why DMIs happen

Mutations are fine separately but clash when combined

Orr-Turelli model of DMIs

Depends on number of mutations, how they interact, and how harmful they are

Do more mutations always mean more DMIs

No—depends if mutations interact

Many mutations but no DMI

Mutations don't affect each other

Few mutations but strong DMI

Mutations strongly interfere with each other

Haerty & Singh finding

Reproductive genes (especially male ones) evolve fast and cause hybrid problems

Burton lab examples

Conflicts between mitochondrial and nuclear DNA; and between sex chromosomes and autosomes

Hybrid problems

Stress response activated, immune issues, low fertility

Polyploidy in plants

Extra sets of chromosomes can instantly create a new species

Why mules are infertile

Odd number of chromosomes (63) → can't pair in meiosis

Do all extra chromosomes have same effect

No—some survivable (Down syndrome), others usually fatal

Gonochore vs hermaphrodite

Gonochore = separate sexes; hermaphrodite = both sexes

Simultaneous hermaphrodite

Both sexes at the same time

Sequential hermaphrodite

Changes sex during life

Gynandromorph

Organism that is half male and half female

How meiosis creates variation

Independent assortment; crossing over; random fertilization

Size advantage model

Being one sex is better at a certain size, so organisms may change sex

Ecdysozoans

Animals that molt their outer layer (ex: arthropods, nematodes)

Key ecdysozoan trait

They have a cuticle (outer covering) that they shed to grow

Early ecdysozoan body plan

Worm-like with no appendages and fluid-based skeleton

Modern ecdysozoans

Segmented bodies, appendages, and chitin cuticle

Tardigrades

Crazy survival ability (cryptobiosis = metabolism stops)

Arthropod exoskeleton

Made of chitin and acts like armor

Why arthropods are so successful

Strong/light exoskeleton, flexible joints, waterproofing layer

Arthropod diversity

Most diverse animal group

Major arthropod groups

Crustaceans, chelicerates, insects, myriapods

Insect body plan

Head, thorax, abdomen

Where insect legs are attached

Thorax

Complete metamorphosis

Egg → larva → pupa → adult

Insect advantage

First animals to fly

Chelicerates

Arthropods with special mouthparts (chelicerae)

Chelicerae function

Used for grabbing or injecting venom

Spider silk

Produced in abdominal glands and released through spinnerets

Spinnerets

Movable structures that control silk release

Why silk is strong

Combines strength and stretch (toughness)

Spider venom

Used to capture prey and defend

Asexual reproduction

One parent, no gametes, fast population growth

Budding

New organism grows off parent (like a bump)

Fragmentation

Body breaks and each piece becomes a new organism

Sexual reproduction

Two parents and gametes → genetic variation

Iteroparous organisms

Reproduce many times

Semelparous organisms

Reproduce once then die

Sexual dimorphism

Males and females look different

Protogynous species

Female → male when needed

Protandrous species

Male → female when needed

Parthenogenesis

Mix of asexual and sexual reproduction

Spider web evolution

Many web types evolved independently (orb, sheet, trapdoor, etc.)

Spider venom evolution

Gene duplication created many different toxins

Human uses of spider silk

Medical materials like sutures

Human uses of venom

Medicines and insecticides

Sexual dimorphism

When males and females of the same species have different traits

Sex-specific trait

A trait that appears in only one sex (ex: only males or only females)

Example of a sex-specific structure

Modified bristles (like sex combs) used for mating behavior

Function of male-specific structures

Often help with mating success (grasping, attracting, competing)

Ancestral condition (before evolution of a new trait)

Males and females look similar with no special structures

Derived condition (after evolution)

One sex develops a new specialized structure

Main genes involved in sex-specific traits

Hox genes (like Scr) and sex-determination genes (like doublesex)

Hox genes

Genes that control body part identity (ex: which leg is which)

Role of Hox genes in traits

They define where a structure can form on the body

Sex-determination genes

Genes that control whether cells develop male or female traits

Doublesex gene function

Turns on male traits and turns off female traits (or vice versa)

Is doublesex active in all cells

No—only in cells that need to develop sex-specific traits

Why this matters

Only certain body parts become sexually dimorphic

Why most cells don't show sex differences

They don't express sex-determination genes like doublesex